I've taken the backs of these off before so I can make fabric covered buttons and glue magnets to the back (or push pins). I just took a pliers and on the loop side squeeze the 2 'post' parts together and wiggle it around. I don't know if that makes sense.http://www.lollychops.com/lollychops/2008/08/buttons-to-cove.html
There is a picture here about what it will look like after they are removed. Squeezing the loop side together makes it easier to remove them from the back side.