I just pulled mine off to install the windscreen clips. 97 Mine have plastic plugs that go into the roll bar. There are serrated dowels that are on the back of the pads that line up and the tight fit is what holds them in place. You just need to pull them very deliberately straight off. I was sure I was going to break something. But nothing did. The key is to pull straight without twisting.
Here is a good link to the install of the deflector that you may be able to glean some help from:
PCA Boxster Register