World of Warcraft Item Upgrades
Upgrades to items can be used to boost the stats of a particular item. Based on the type of upgrade it could boost an item's Mark Level or Rarity and boost additional stats.
Each item has a track for upgrading it. Each upgrade increases the cost of the following one by a specific amount.
Item Level

When an item gets upgraded, its stats increase in value. This value is the total of all of its leveled up benefits (attack magic attack, attack defense). Upgrading enhance equipment can be expensive, dependent on the upgrader and what kind of upgrade you decide to do. This is because of how many perks need to be replaced to allow the item to get upgraded.
The level of an item is a widely used measurement of power and is visible on all item tooltips. It is also used to limit how much PvP gear players can use, since PvP is limited at lower levels. The average level of an item can be found in the character sheet.
Using the item level can help players compare the power of equipment when they decide to buy or sell. It's an excellent indicator of an item's quality and the amount of damage it is capable of causing. The item level can also be used to evaluate items when examining a vendor's inventory.
The item level can be seen by pressing the ALT key on PC or using the left stick (L3) on XB1 and PS4. This will display the full description of the item, including its ilvl. It can also be found by hovering over an item using the mouse cursor and typing /itemlevel in chat.
There are a variety of theories on how the item level is calculated. One theory is that the item level is a number that comes from a formula that calculates how much an item's stats are worth. It considers that different advantages are valued differently and that gems in the sockets increase the value of the item. This can result in a calculated value for the item's ilvl which is usually quite close to Blizzard's real item level.
This isn't the only factor that influences the level of an item. The degree of the area in which the item was dropped can alter its stats. For instance it can add a level to the item's haste, or crit rating. Items that drop in higher-level instances will have higher ilvl.
Item Stats
The stats of an item are a major component of what determines the value of an item for players. The game uses them in many ways to encourage players not to limit themselves to a single weapon and to motivate them to try out other weapons. The stat mods of a weapon boost the base stats. These stat mods are then increased by the player's level.
The upgrades to an item can increase the stats of an item. The rarity of an item determines its upgrade cost. A white or grey item, for example, will only be upgraded once and items with rare tiers may be upgraded multiple times with more expensive costs.
Affixes are a different method to alter the stats of an item. These are special stat boosts that can be added to an item by the player and are available in all sizes and shapes. The affixes can be used to give the item additional damage, or add a unique capability to the item (such as reviving dead or cutting down cooldowns), or make the item unique by putting an additional name to the item.
Currently, all affixes can be rerolled by selecting them from the upgrade window and pressing the green button, which is accompanied by circling arrows. This will cost a certain amount of gold and other items. They can also be used as upgrade gauges, similar to other methods of rerolling.
Players can upgrade an item with specific stats, or reroll the affixes. The range of stats determined by the item's level. However each item will contain at least one stat within the range, unless they are an exclusive item, or an item that has a God Roll from a raid boss.
Another thing that could be changed is the possibility to upgrade equipment without having to reroll the affixes, or choose which stats to enhance. But as with base equipment, this would need to be performed on a per-item level, and the item compare interface wouldn't show all possible stats gained or lost at once.
Item Luck
The Luck stat of a player boosts the chance of finding items, the properties that are generated by loot, and the strength of these properties. It doesn't, however directly affect damage or the ability to upgrade items. It provides players with the chance to upgrade equipment earlier in the game. This is especially beneficial in the early game, because players tend to put weapon scaling and defenses above raw damage gains.
Luck can also boost the likelihood of upgrading items at the Blacksmith. This is not to be confused with the Blacksmith's overall chance of upgrading which increases with each level and can be further enhanced by using an anti-material such as a Scroll of Strength or a Jewel of Blessing.
Weapons, armor, and shields can spawn or be crafted by using the Luck property, which has an initial value of 40. These items can be upgraded with golden ingots, spined leather, or oak boards (depending on the material of the item) to give +40 Luck, or to increase the Luck of an item, up to 140.
Certain items, such as the weapon that is infused with hollow can also be crafted to increase the damage dealt by any ability that deals damage by 5%. These items can be bought from the shop, or they can be made using the correct ingredients.
Item Failure
Upgrades to items can be a costly process and not every upgrade will be successful. Cash shop items can be used to increase the chances of success for an upgrade, or to protect players from losing their item if it fails.
The success rate of an upgrade is displayed in the Honing UI. The percentage is the probability of successfully upgrading an item. This can be increased with Additional Materials or Special materials. There are limitations to the extent to which success rates can be increased and the probability of a failed upgrade cannot be greater than 100%..
The success of an item upgrade is also affected by the luck of the item. Each item has an average success rate of 25%, and each item with Luck increases that chance by an additional five percent.
The upgrade overlays of the item are rendered above items in the inventory. This can obscure enchantment effects and other effects. If you wish to disable the upgrade overlays, the config option decoration.renderUpgradeOverlays can be set to False in the Item Upgrader CORE client config.