Every game you play earns coins for your avatar, displayed on the avatar menu. Use these coins to rent Avatar upgrades, which currently include...
The Speed Racer (Racecar) has a higher top speed, but requires you to pedal harder for it!
Homing Missiles (Chopper) allow you to paint rather than aim at turrets.
The Golden Pegasus (Pegasus) increases your flight ceiling and stamina.
Tank Flags (Tank) to personalize your ride.
As with avatars and levels, you can expect more upgrades to appear on a regular basis through automatic updates. Upgrade rentals cost coins for every game play, so use them wisely! You can also purchase upgrades for permanent use on PlayStation Network with credits you can buy (with Steam purchase capability planned for the future).