Head Blacksmith Ferris:
Equipment upgrade is available for rare items as well as normal weapons, armor, and accessories. You can only upgrade enchanted items, and you need the necessary materials.
Keep in mind that for all upgrades (excluding rare upgrades), weapons must be enchanted at least to +12, armor to +10, and accessories to +8.
Also remember that each upgrade type has a certain chance to fail and that you cannot upgrade weapons with Augment or Rune effects.
Remember that for gloves, boots, and helmets of B-grade and above, upgrades are only possible when the armor is sealed.
Lastly, the items you obtain through the special armor upgrade are always sealed.
Upgrade type
Rare upgrade - Upgrade paid and rare items to a higher grade
Normal upgrade - Level up D- to A-grade items
Special upgrade - Obtain S-grade items (includes exchange chance)