You can either do a few races with a design and a pop up will occur after a few races allowing you to like the paint-job, or for a faster way:
Go in Career mode, select a car, choose upgrade, then press the view button
to go into setup manager. Choose load setup, choose one of the setups and download and install it.
It will kick you back out to the upgrade shop menu, so go back into setup manager, choose load setup again, hit the
right bumper to take you to your tunes, press the
a button on one, and choose the like option.
Achievement Get!