Depends on whether you have a snap-in or a clip-in. If it's a clip-in, just remove the clip on the bottom. if it's a snap in, then you need to pop it out. A hammer will work if you have something round and hollow that can support the lip but allow the center part to pop out. Otherwise you can hold it in your hand and slam the bottom down on a table pretty hard and it should pop out.
Or just buy new ones at $1-2 each.
Why do you want to take it apart? If it's sticky, just squirt it with Windex, actuate it about 50 times or so, wipe it dry, then use...