I highly doubt that your celeron is really even running that hot to worry about replacing the thermal pad with thermal paste, but if your like me, when i know there is a better cooling solution (albeit 2-3c) I'll do it. Heres how i went about successfully removing the thermal pad and applying thermal paste:
1. With the cpu being thoroughly stuck to the heatsink by the thermal pad, CAREFULLY
pull straight up on the heatsink cuz your processor is gonna come out at the same time without letting you pop up the locking lever. Straight up, no twisty twisty or your pins will be munchy munchy.
use a small thin flathead screwdriver to GENTLY pry up the cpu from the heatsink.
3. Once the two are sperated, use a NEW
razor blade to shave off any remaining thermal pad from both cpu and heatsink being carefull not to gouge the surface of the heatsink.
3. Replace the cpu into the socket relocking the mechanism. Apply a thin line (in red below) of thermal paste across the back of the cpu and using a credit card or similar spread evenly across entire cpu. Make sure no paste smears over the edges, gotta keep it entirely on the cpu, lol.
4. Replace heatsink squarely onto the cpu so that there is no slipping and sliding around on it. This causes pastes to get slimed over the edge of the cpu and could cause arcing if it were to get on any circuitry. Once the heatsink is squarely on, slightly push down on the heatsink and twist EVER SO SLIGHTLY
by about a 1/2 degree left then back again to close out any gaps between cpu, paste and heatsink. Lock the heatsink into place and bingo
there you go.