Use the electrical cleaner as suggested by drea.drechsler it'll shift any paste, even out of the tiny holes but a few words about the stuff:
If you have any breathing issues such as asthma, DON'T use this stuff, you could trigger an attack, and DON'T use it indoors if some one else living there has breathing difficulties or asthma-for obvious reasons.
Don't use it on any energised electrical systems or components, even a tiny spark can ignite some of these cleaners!
Most are very flammable, use it outside if at all possible, if not use it in a very well ventilated room/shed/outbuilding well away from any sources of ignition.
To reduce the mess and amount used, lay the system on its side and wrap a DRY cloth around the socket to contain any overspray, if the spray comes with a plastic tube, use it to direct the product at the hole/s in question and remember; short, controlled bursts, drenching the motherboard and CPU socket won't achieve much. This will also keep any paste particles contained making them easier to remove using said dry cloth.
Dab the cloth, do not ever drag a cloth of any kind over an electronic circuit board, even a paper towel will snag on the components and leave chunks of difficult to remove fibre behind while a woven cloth can snag and pull off tiny surface mounted components.
The stuff evaporates quickly, is non conductive and harmless to electronic components, so don't worry if you get it all over the place, just stand the system upright in a warm place for about 1/2 hour to be really sure the solvent has dried out fully before reassembling the system, just bear in mind my points about breathing issues, though.
Some may leave a slight stain or mark, ignore it, any staining or marking will be totally harmless.
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