Hello... lay some non conductive material down first... and do not have socks on with rubbing to the carpet... don't be creating a static charge when handling your graphics card... also if this is a warranty item do not peel back any graphics stickers on the card for access to the philips head screws on the bottom...
Pretty easy after that... remove the screws to the fan assembly... and using your hands pull the fan assembly from the GPU and thermal paste... Once removed... determine and collect any extra thermal paste for re-use... there might be some on the memory chips too or thermal pads... do not try to destroy them or remove them...
Use rubbing Alcohol to wipe clean the GPU and heatsink... inspect contact surfaces and inspect clearence and re-fit the fan assembly to the GPU... Look for any fitting/obstruction problems before re-appling thermal paste back on...
If the thermal paste has hardened and not re-useable... get new from local store... it should always be wet and plyable for the best thermal conduction... the least thermal paste the better... it is used to filled the air gaps between the metal parts... That is why people will take time to finely sand and polish their heatsinks and CPU/GPU's... and get the best metal to metal contact for maximum heat exchange.
if no obstructions and good fit... no massive space between the GPU/memory/heatsink... re-apply just a thin layer to all the mating components...rubbing it into the GPU and Heatsink... even a dab on those memory thermal pads, if your card used them...
Check fit agian and determine if the thermal grease is in contact with every component... if good re-assemble and re-install in your computer.