How to Install an M.2 SSD in the Lenovo ThinkPad T440s | Laptop Mag
Lenovo ThinkPad T440 m.2 SSD and 2.5" SSD Install (how to + test run) - YouTube
BEWARE: Lenovo Thinkpad L15 Gen3 SSD is practically un-upgradeable. Laptop comes with 256GB and bigger SSD is too thick to fit. There also goes a cooling plate on top. : r/thinkpad