Which radio do you have, the six button or the five button? The six button ones it says right on the fuse holder "10 Amp." But that's assuming the cable has not been replaced. The five button, Delco radio used a 14 amp but a 10 amp would likely work just fine on that model.
As far as getting the fuse out, the holders are spring loaded to keep the fuse snug and making good contact. To remove the fuse, push the ends together while turning it and it should release those plastic tabs.