A hot air soldering station must be used for desoldering.
Mine is a very cheap (approx. 40€ from ebay) model name you can see on the photo. I have set it to 320°C:


On this picture I tried to build a heat shield with a piece of aluminium foil to protect the other parts. But this proved to be not so advantageous, because the hot air is moving under the foil and the nearby components are desoldered. So it is better to work without aluminium foil.
The hot air is used to heat the "feet" of the processor (and thus also the circuit board) in circular movements until the solder is liquid (approx. 5 min).





And can then remove the processor:


The next step is to place it on the programming adapter and solder it on:




Then check if there are no solder bridges or unsoldered pins: