It's really straightforward; just follow these instructions...
Step 1: Remove Your Old Air Conditioning Knobs
A cloth and a pair of pliers are all you need to do this. Sometimes just pulling will do the trick but if not, place a cloth over the knob (so as not to damage or break the existing knob) and grip firmly with the pliers. A good tug and a bit of wiggling should be all that's required to remove it.
Step 2: Line up the first New AC Knob
Pay close attention to the back of the new part. They usually have a flat edge or clips which only allow it to be installed one way. It might help to turn the AC fully off or on so that you can easily line it up with the controller stalk and prevent it from moving, after which you should be able to align the new knob and push it on a short way.
Step 3: Push the New Knob into place
Once you are absolutely certain that the AC stalk on your dash is correctly aligned with the connection on the new knob, push it slowly but firmly into place. Some have clips (depending on the model of car), which you should hear click into position. Repeat until all new knobs are in place and hey presto: a stylish new look to your air conditioning dash!