Read then re-read and read the instruction again. Take your time. No reason to rush. Take everything one step at a time. Check the Gelid website, Youtube, or google search for instructional videos. Take apart the old heatsink and see how the new Gelid fits on before actually installing it. See how it makes contact with the gpu so you know where and how much thermal paste to apply. Use alcohol swabs or electronics cleaner to clean all surfaces of the GPU before installing the Gelid. Use jersey cotton or electrostatic gloves if your paranoid about fingerprints and/or static discharge. MOST IMPORTANTLY, take your time and FOLLOW the instructions!
It's really not that hard. Take you less that 30 minutes start to finish. Good luck!