Screws? An AMD HSF usually just has the clips. If you can't get a thumbnail down there to do it, AND if you are very careful, you could use something like a small-diameter screwdriver to press down on the clip in order to release it.
If the thermal paste you used is non-conductive, you're probably okay. If it isn't, once you get the HSF off and CPU out, you could clean the pins with a Q-tip (cotton swab) dipped in 91% isopropyl alcohol. If you got it down in the socket, you could use the same 91% alcohol in a squirt gun to forcibly irrigate the socket. Just be sure to let it thoroughly dry afterward.