Superstars can be improved by acquiring copies of the same Superstar, as well as applying Trainers.

Superstars can be acquired at several rarities: Common (Bronze),

Uncommon (silver) , and Rare (gold).

All Superstars are initially acquired at a 1-Star rating. After acquiring enough copies of a Superstar, or applying enough trainers, the Superstar will be ready to be evolved.

Evolving a Superstar will increase the Star Rating of the Superstar by one level (a 1 star Superstar will involve into a 2 star Superstar. and so forth

In order to create a 2 Star Superstar your user score must also be at 2 stars. This is true for all star rating evolutions. The higher your player level is, the more stars are available to upgrade your superstars.