First, I'd like to emphasize that you should leave any dismantle or component exchange to your authorized Asus service center. There might also be some problems if you've change some parts of your notebook and then you try to claim the Asus warranty.
But on the other hand: I've replaced my notebook's memory module, by myself. Then, after half a year, I had to send the whole notebook for HDD exchange to servis center - and there was no problem (but I removed the mem before sending just to be sure).
How to dismantle/disassemble the notebook
There are 3 lids in the back of A6R. The HDD lid has only one screw, the others have two. The HDD lid can be removed easier than the others. The Mem/WiFi lid you need to push right and than pull it up, the CPU and fan lid you need to push down and then lift up.
The memory replacement should be easy for everyone. If you already have a module in the socket, simply lift it up - you dont need to do anything with the holders. After the module reaches over the holders, simply pull it out of the socket.
To insert the new module, check the correct module position (empty pin position),and then (gently) push the memory to the socket. It should go easily, with no force needed. Then, push the memory down, so the handles clip on the module holes. See the picture for details and instructions:
I don't know if it is worth to replace the CPU of this notebook, since now for the price of a new CPU you can almost get a new low-end notebook. Overmore, I can't see any easy way how the cooling pipes could be removed from the CPU. Anyway, I haven't tried to do so, so if anyone did, please, post a comment below.
Fan replacement
It can be done in few minutes. What you need is either a fan (the rotor part) that is compatibile with the one that is inside the current fan and has the proper connector (or remove the connector from the original and resolder it to the new fan) or a branded Asus A6R fan.
Using unbranded fan seemed too difficult to me, so I wrote an email to my local ASUS distributor, asking for a new fan component as a spare part. They found the proper one and send it to me for about 30$ in 2 days.
Then the replacement was easy. I simply unscrewed the two screws holding the fan in its position, detached the power cables from board and removed the tape covering and holding the ribbed heatsink and the fan part together and removed the whole fan component. The inserting procedure is the same, but reversed.

