To remove your old buttons, simply use a pick. Place the tip of the pick between the bottom of the button and the IHKA panel and gently pry the button outwards -- the bottom of the button should then "give" and come away from the panel. Pull down gently on the button and the two tabs holding it in at the top will release, and you can remove the button. You'll have to be careful to mind the clear acrylic insert which is the light carrier (if it is one of the buttons that has a light on it, or one one of the blue or red arrow buttons).
If you don't have a pick handy, you can use your finger and push up against the bottom of the button while pulling the bottom of the button away from the panel. It will "give" and come off the panel once you use the right amount of pressure. Remember, if you already have your replacement button from IHKAButtons.com, you don't have to worry about breaking the old button.
To install your new buttons, gently press them into the panel starting with the top half of the button first. Once the top half is engaged, you can swing the bottom part of the button down and into the panel by simply pressing the button as though you were using it while driving. It will snap into place.
For the fan speed button with the + and - symbols, the installation is slightly different in that you don't need to put the button in with as much of a top-first motion -- in other words, the button can go almost straight into the panel. However, putting the top part of the button in first still helps to ease installation.
If you have any questions, please don't hesitate to send an email before attempting installation of your buttons.