Legend of Zelda: Tears of the Kingdom item level upgrade Upgrade Guide
The upgrade feature for items allows players to increase their armor, weapon, and Item Upgrading trinkets' quality and receive extra bonuses. They also offer a variety of cosmetic effects.
Upgrades can increase the value of most items, but there are some exceptions. For example, a perfectly rolled eth titan can be worth 20x or more than its counterpart that isn't upgraded.
Rerolling
Rerolling allows players to switch a weapon upgrade or armor upgrade with one with different stats. This feature can be used to gain more value from an upgrade, since it doesn't affect the item upgrades’s level or bonus. To roll an upgrade again, click on the box icon, and upgrade Items then choose the "Reroll" option. The upgrade you choose to reroll will be random, and the original's extra bonuses will not be restored.
Rerolling is popular in many gacha games, including Genshin Impact.