You can strengthen your equipment by leveling it with gold. The higher the rank and level of the equipment, the more gold you need when upgrading it. At first, you can only level your equipment so much. However, after you upgrade “Potential Flex” in the Technology Center, you can level your equipment up to 30. You can even level equipment all the way up to 60 if you raise the Specialization techs (Melee Specialization, Ranged Specialization and Corsair Specialization).
You can raise the rank of your equipment, but first you must get some materials. Once a piece of equipment reaches a new rank, it loses 5 levels. There are 7 ranks altogether. High rank equipment offers better stats. High rank equipment can only be worn by high level officers.