In SF Girls there are 5 upgrades that you can make to an agent:

1. Level up: You will need Agent EXP material to increase an agent's level to a maximum of 120 at 6 stars. Each level provides a small increase to the damage they can inflict.

2. Skill upgrade: You can use skill materials to increase an agent's skill level to a maximum of 60 at 6 stars. Each level increases the effectiveness of the skill and also it can increase/decrease the cooldown duration of a skill.

3. Promote: By default, the agents are between 1 and 5 stars. With the promotion system, you can increase their number of stars by one to a maximum of 6. To promote an agent, you will first need to level her up to the current maximum cap. However, keep in mind that she will lose all the current levels in the process (skill levels are not affected by promoting).

4. Evolve: After you recruit an agent you can still receive shards for that specific agent. You can use the extra shards to greatly enhance her combat capabilities by evolving her.

5. Weapons: Each agent can have a weapon and a gadget equipped. Even if not present in the primary upgrade menu for agents, adding weapons greatly enhances combat capabilities. You can equip weapons from your Inventory.