You can upgrade Equipment’s Grade level by “Forging”. Each “Forging” equipment must be at max level 30 and need the same type of equipment which is the same grade level as materials.
By selecting equipment in your inventory and touching the “Forge” button, you can access Equipment Growth Interface which you can Level Up, Enhance, Forge and Combine Stone for your equipment. (Or access “Forge” by touching the Main menu button on the top-right screen.)
When Forged, both main and additional material equipment’s options will be combined together. Failure forging causes material equipment to be destroyed. (Can be prevent by using “Polish”)
For “Heroic” and “Ancient” Equipment needed a specific Forge Stone as a material. (Guarantee 100% success rate.)