Obtain more Car Credits using Multiplayer Tokens in the Marketplace. You can also randomly get them by redeeming Supply or Premium Points in the Imports.

Once you’ve collected 20 Credits for a certain car, it will then be delivered in your Garage. 

By tapping on My Cars on the upper center of the screen, you will be redirected to your Car List and from there, you will be able to upgrade and customize them.

Continue upgrading your cars by collecting more Car Credits from the Imports.