I am not sure about the upgrading part, but you certainly can replace the SSD chips. However, the NAND chips are soldered onto the board, so you will need soldering skills and a rework station. I myself haven't done a NAND replacement yet. If you are looking for a NAND chip replacement, look at the SoFix MacBook repair website (masterliuonline.com). They have original NAND chips, and they have A2251 model.