Pretty easy - get a long cable tie, put a bend in the end and post the folded-back tie down one of the inside holes of the vent, with the cabletie held so that as it goes through the hole and expands, the short end is facing the outside edge. Pull it back and you should have a cable tie wrapped around the vent. Click it together to make a convenient handle, then repeat the process so you have 2 evenly spaced cable tie loops on the vent. Jerk it hard towards you. Central vents can be a bugger to get out so worth bracing the center console with your hand to prevent flexing.
Once out, file the metal clips on the inside of the holes with emery paper and give them a shot of silicone spray lube to make it easier next time.
When you've got them out, you can carefully split the balls from the surrounding tube and you'll notice the foam pads have gone flat. You can pad with small strips of electrical tape.
If you can't separate ball from tube, then just rotate ball as far as it can go in one direction and apply a small strip (about 5mmx20mm) to the side of it to achieve the same effect.