There are two tabs holding the retainer for the bar in place. Gently pop these toward you with a spudger and they'll slide up from their own tension. Note: the retainer will likely stay attached to the bumper assembly, but must be removed from the main controller assembly before proceeding to the next step.

Once the retainer has been released, again use the spudger to gently pry the buttons outward and upward (in the direction of the arrow in the image) which will release them from another clip. Do this on both sides.

As user Shane Muir has pointed out, please be careful due to the fragility of the retainer in this step. It can easily be broken.