Superstars can also be improved with Gear. You can get Gear from:

Stats are improved by equipping gear. Each piece of gear provides different bonuses. 

Each Superstar has six gear slots. To equip gear go to the roster screen and then select the Superstar's profile. Once gear is equipped, it cannot be removed.

Gear starts at level One. When all six pieces of gear have been equipped, the Superstar can advance to the next Gear-Level. When this happens, current gear will be absorbed into the base stats of the Superstar. The bonus will remain but the gear slots are then empty again.