Equipment upgrading allows you to change the grade of weapons, armor and accessories. In order to do that, you need to collect all necessary materials.
But unfortunately shields and sigils cannot be upgraded. Weapons can be upgraded after +7 enchant level, armor - after +6 enchant level, circlets, Dragon Skin Shirt, Kaliel's Bracelet, La Vie En Rose's Brooch and Artifact Books - after +5 enchant level.

Upgrading Equipment

Item for upgrade	Result
Apocalypse (blessed)	Specter Weapon
Twilight (blessed)	Seraph Armor
Specter (blessed)	Helios Weapon
Seraph (blessed)	Eternal Armor
Helios (blessed)	Krishna Weapon
Eternal (blessed)	Leviathan Armor

Required materials

Weapon	Armor
Blessed weapon	Blessed armor
R-grade Gemstone	R-grade Gemstone
R-grade Crystal	R-grade Crystal
Crystal of Determination	Crystal of Protection

Accessories

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Accessories	High-grade Resources	Top-grade Resources
Circlets	Noble Upgrade Stone	Radiant Upgrade Stone
Dragon Skin Shirt	Noble Leather Upgrade Stone	Radiant Rind Upgrade Stone
Kaliel's Bracelet	Crystal of Dawn	Crystal of Dawn
La Vie En Rose's Brooch	Crystal of Dawn	Crystal of Dawn
La Vie En Rose's Brooch	Crystal of Dawn	Crystal of Dawn