@albye
Normally those computer enthusiastic will recommend you to get arctic silver thermal paste / compound.
ifixit sells those
[product|IF179-010]
http://www.arcticsilver.com/as5.htm
another alternative which I feel is quite good too…
https://eu.coolermaster.com/en/cooling/thermal-compound/mastergel-pro/
'''Instructions to apply thermal paste'''
http://www.arcticsilver.com/pdf/appmeth/int/vl/intel_app_method_vertical_line_v1.1.pdf