Go to the Inventory menu and tap Merge to create a new and powerful piece of equipment. Tap Info to see the merge rules for each rarity. In order to merge your equipment, you must have at least two or three items of the same type. Choose the items from your arsenal to get a new enhanced one. Higher rarity equipment is always better than lower rarity equipment, and opens up more possibilities. Tap Merge All to automatically merge all common, good, and better equipment. Note that S-grade equipment has different merge rules.