Upgrading your car in Rival Gears is done through the "Upgrade" Screen.
Each Car contains 15 Modules.
5 Standard Components
5 Rare Components
5 Elite Components
12 of these modules are universal parts that can be fitted to all cars in that class and 3 parts are Manufacturer specific parts for that class. Each module is made up of 5 component parts, that can be collected in a variety of ways through playing Rival Gears or bought from the Upgrade screen.
When you own 5 component for the same Module, you can use them to create and fit the Module to your car.