You can remove the cooler then clean off the paste with some kitchen paper soaked in isoproponal (or use tissues).
You can use a small screwdriver to put a rice-grain-size blob of thermal paste on the CPU in the middle. Also use it to straighten any bent pins.
Try it without paste so you can practice it.
Renew the paste every 12–18 months. You can get some $2 GD900 paste on www.ebay.com It's as good as some of the top pastes.
You can get some $2 GD900 thermal paste on www.ebay.com It's as good as some of the top pastes.