Earn the indicated number of medals to unlock the corresponding upgrade.

Crystal ball: 5 gold medals.
Digital amplification: 5 gold medals.
Double cash: 15 gold medals.
Doubleranga: 10 gold medals.
Dreadnought: 5 gold medals.
Exploding darts: 10 gold medals.
Frag bombs: 10 gold medals.
Healthy bananas: 15 gold medals.
Monkey tycoon: 15 gold medals.