It took far too long for Microsoft to release an upgradeable (and partially repairable) Surface. Even then, on the few recent devices with the capability, it's just the SSD that can be replaced. However, the tiny M.2 2230 drives that Microsoft chose are hard to find, with upgraders having to scavenge them from USB SSDs and from Xbox X and S storage expansion modules. .

Link: I upgraded the SSD in a Surface Pro X. This is how it went
via http://www.zdnet.com