To do it properly, the glass needs to be removed. 2 Torx 20 screws to remove from each side, bit fiddly but can be done. You will then have access to the sun blind. It held in with 3 clips. Carefully unsnap each clip by moving the tags towards the front of the car. Remove the blind. The blind is sprung loaded, you can re-tension the spring by winding it back up. Tricky part is keeping it all together to refit as, as soon as you let go of it, the spring will unwind itself. Probably a job for 2 poeple, one either side of the car to guide it back in and snap the lugs into place.
Hope that helps and good luck.