[WindowsCentral.com]

Valve doesn't want you to do this but you can certainly try.
What you need to know

[LIST][*]Valve has published its own teardown video of the Steam Deck.[*]Opening it up isn't recommended, but it doesn't look difficult.[*]The SSD is replaceable, though it's not the regular size you'd get for a desktop or laptop.[/LIST]
Much has been made of the Steam Deck being a handheld PC and what you can do with it even if you shouldn't. Being a PC gives much more freedom compared to something like the Nintendo Switch.

Full story from the WindowsCentral blog...