Lie on your back with your knees bent up and feet on the floor with the foam roller sideways underneath your upper back. Place your hand behind your head to support your neck. Gently let your upper back arch backwards/wrap over the foam roller. Try not to let your lower back arch, you want to encourage the movement to happen through your upper back. Think of doing a reverse ab crunch where you control the movement with your abdominals. Arch over and the foam roller and then bring yourself back up to neutral. Once you have repeat this a few times slide your body up or down an inch so that the foam roller is now under a different spot in your spine and repeat.

Regression: If the pressure of the foam roller is too uncomfortable, try doing the exercise over a rolled up towel, it will be softer and the angle less acute and you can work towards the foam roller.
Progression: Try switching between having your elbows drop out to the side (with hands still supporting the head) and elbows pointing directly up to the ceiling.
Alternative: Put the foam roller on a 45 deg angle (as shown in video) to target one side and the rib joints.