Disassembling the keys appeared to be easy, after two tries 🙂 Now I fix a stuck key in 30-60s.
There are just a few things you should know, the most important is that you should be very gentle in order not to break any of the delicate plastic parts. Don't try it if you don't have appropriate manual skills. Or if you still have the guarantee to lose in case of physical damage you can make trying to fix the keys yourself.
There are two moving parts - the key itself and the inner lever set. You can take off the key by pulling first its top side (the one closer to the screen). You can do it by pushing first the key in the opposite direction to make some space on the top side, putting there some flat piece of plastic or nail to pry. Try to lift just the key, so don't put the pry too deep, since you could also reach the key levers that should stay in place. You will hear 2-4 clicks of disconnecting joints, depending on the key size. Once all the top joints are open, the key can be lifted almost vertical when its bottom hooks disconnect from the joints (this is why you should start from the top side - the hooks could break if pulled first). You can then remove the key and use compressed air to clean the key socket. The small function keys have hooks on the right side, so start opening them from the left side. After cleaning just place the key with the hooks first, lay it down and push gently - you should hear the clicks of connecting joints. The key should work as a new one, of course if you managed not to break anything 🙂
If you want to clean also the lever set, which is more risky, you can take it off by pushing them towards left and prying up the left side. Why left? Because the lever is asymmetric - the hooks on the left side are slightly shorter (less than 0,5 mm?) than the right ones.
Sometimes when you lift the key, it appears that the levers came out along with the key. You can put the key with the levers (or just the levers) back but first put down and align the right side of the key/levers, pushing gently down so that the longer lever hooks find their place. Then push the key/levers left and down (on the left side) so that the left shorter hooks click. That's it. Hope this helps someone.
(Last warning: be gentle. I broke one lever hook the first time I opened the key, this is how I learnt they are asymmetric.)