How to clean PC fans

As the previous poster mentioned, if you remove the cooler (even better if you can remove the fan), you can then clean it really well with a cloth. If your fans are making a lot of noise now than in the past even after cleaning them, you may need to oil the bearings of the fan.

Also, yes, there is a chance you may need to change the thermal paste because it can dry up but that usually happens after many years (5-10+) though I haven't replaced my thermal paste in 8 years here and my temperatures are still pretty good (depends on the thermal paste quality).

I used an air compressor machine to clean the fans of my PC (overkill) but very effective.