unfortunately I have not taken any pictures, because I had not the slightest confidence in the outcome! However, I can summarize the process with pictures found online:
1- the memory chip (which is on top of the processor) is the one with the red dot on it; you must also remove the metal shield around it, which is fitted with just clips, so a small screwdriver and some care is enough to remove it;
2. you must heat up the chip with a hot air rework station; I also recommend to cover the rest of the board with kapton tape (or, at worst, with some aluminium foil);
3- use a thermocouple if possible; if you don't have it, monitor carefully the melting of the memory chip. Keep in mind you have to remove the memory only, not the entire chip (but the memory chip, being on top, is the first thing to come off);
4- using a needle or a thin razor blade, gently leverage one corner of the chip until you feel it softening and finally coming off;
5- after removing it, you must very carefully clean the pads from any glue left on them (yes, the memory is also glued!). The pads are not too delicate, however exert maximum care, you do not want to rip any of them off; I personally used the scalpel tip of my soldering iron to clean and level the pads;
6- use isopropyl alcohol, acetone and some sandpaper or a pencil rubber to clean the pads from any dirt and oxidation; you must end with some very clean pads, as in the picture (of course pads will not be gold but silver);
7- spread some gel flux on the pads and place the new chip on them, carefully aligning it with the processor underneath (careful about pin 1!);
8- heat up the chip again with the hot air gun; look at it from the side, until you see the balls melting and the whole chip settling down in the correct position;
9- remove hot air and let it cool nice and slow;
Please note that the process is extremely risky and complex; if you need to read the above steps, probably you should not attempt it; but if you succeed, results are worth the effort! The whole process took about 1-1.5 hours (I do not know exactly).
Next step will be to upgrade storage space (someone has already done it, if I remember correctly)!