Your Cosmoloid's grade affects their maximum level and when your Cosmoloid is upgraded they get a boost in their stats. The rank of a cosmoloid also affects the amount of spheres the unit can use.
To upgrade your Cosmoloid, he/she needs to be at max level and "Trigger" items are needed. You can obtain trigger items by exchanging for them in the "Cosmo Piece" interface, completing daily or weekly quests, and purchasing them from the in-game shop using your RT or FP.
Cosmoloids require specific triggers to rank up. Certain units will have a limit to their maximum rank.
|Max Level||Sphere Slots||
|A||30||9||2 Tetratriggers, 1 Hexatrigger|
|S||40||12||2 Tetratriggers, 1 Hexatriggers, 2 Octatriggers|