WoW Upgrades - The Item Upgrader
Upgrades will give you a boost to certain stats. Each upgrade increases the level of the item by +3. Each upgrade also increases an unspecified substat.
Upgraded gear is generally more valuable, unless it is not required by nature (like FB sorc shields) or has a large variance in stats (like eth Titan weapons). Upgrades aren't as useful for those with higher variance due to the need to roll a perfect version.

Recycle Points
The item upgrader allows players to upgrade their gear by transferring the currency to an NPC. Upgrades can be applied to any type of armor or weapon. The item used to upgrade the item will be consumed and can't be used again. Upgrades can also be applied to enchantments.
You can upgrade your gear anytime by visiting the upgrader in any major city. To keep your gear current it is recommended you visit the upgrader each couple of weeks.
Upgrades will cost more, based on the level of the item, however, they are always cheaper than buying new equipment. Upgrades such as upgrading a Benthic chest up to ilvl385 will cost you 20 recycle points. If you purchase a similar item, it will cost you 105.
Valorstones
Upgrades are functional items which can be used to improve the quality of weapons and tools, armor and other items. They can be purchased by players through NPCs that sell upgrades to items in exchange for a variety of currencies, and may also be found in random treasure lists. Once purchased, an upgrade is able to be applied to any tool, weapon, or armor. The button will display a preview of an item's next level of upgrade, if there are enough materials.
The cost of upgrading is based on the item slot and current item level, with weapons costing more than bracers or gloves, for instance. Each upgrade cost 15 Flightstones and a few crests, with some upgrades having a discount to reduce the cost of the Flightstones or the crests used. Once an item is upgraded to a certain degree, it can be downgraded and sold to the upgrader at a lower cost.
Item upgraders can be found at many locations, including the main island as well as some outposts. The NPCs provide an upgrade discount as well as a chance to obtain a new upgrade recipe. The discount on upgrades increases depending on the amount of items that are being upgraded. It can also be increased by having players complete some specific achievements or complete quests.
Icewind Dale does not have an item upgrader at the start, unlike Cromwell from Baldur's gate II. The NPCs that can assist with upgrades are only accessible through a variety of methods. This is both a benefit as well as a drawback.
In Season 3, several new features have been added to the upgrade system. Once a player obtains an upgrade to a particular level for an item in an armor slot, upgrading further items to that level will be less expensive, even when they are part of an entirely different set of gear.
The amount of Valorstones needed for upgrades is decreased, and the discount is affixed to all accounts. The amount of Harbinger Crests needed to upgrade is cut as well, but is only available once certain milestones are reached.
Crests
Players have several options for upgrading their equipment in WoW. They can choose to use Flightstones that are a general upgrade currency that is available to all players, or crests, which are more specific and consumed during upgrades at specific levels of the item. Crests are an essential part of the Dragonflight gear progression system introduced in 10.1, and come in four ranks.
First, you must be aware that the crests can only be purchased for equipment that is of a particular rank. Each rank has an upgrade path that is different. The simplest and most straightforward upgrade path costs 15 crests, while the most complicated requires as many as 20 crests, based on the type of equipment that is being upgraded.
Players can earn crests by finishing content at the appropriate level, whether that means walking around and doing outdoor activities for gear of lower tiers, raids or dungeons with any difficulty for higher-tier items or Mythic+ dungeons or heroic raid bosses for endgame gear. These crests can be exchanged with an item upgrade r such as Cuzolth or Vaskarn, in Valdrakken to upgrade the item in the proper steps and routes.
The new currency system isn't too difficult to use, but it does bring some modifications to the upgrade process. When a piece of equipment reaches the highest level of upgrade for any rank (Explorer or Adventurer), it will no longer require Flightstones. This change is intended to allow players to get their equipment up to the highest ilvl possible on all their characters, instead of relying only on seasonal loot.
Another notable modification is that crests have one use and it's crucial to make use of them in a responsible manner. It is best to put your Whelpling-rank Crests on the highest-quality gear that you can find and save Drake and Wyrm Crests for the next set of upgrades. This is particularly true for items like rings and trinkets that fill multiple slots on the character, that will be able to take advantage of the discount for all accounts when all of the slots are filled with top-quality equipment.