HOW TO UPGRADE / REPLACE SSD for STEAM DECK 64GB EMMC and INSTALL OS! - YouTube
Steam Deck SSD Replacement - iFixit Repair Guide
Upgraded the 64gb to a 256gb, went pretty smooth and simple, only problem I ran into was removing the side clips of the decks casing, it just wouldn't budge. : r/SteamDeck
How to Upgrade Your 64GB Steam Deck's Storage Capacity Now to 512GB for Just $60
Valve boss confirms the Steam Deck SSD is upgradable - Hardware - News - HEXUS.net