TUTORIAL: Lenovo T440P M.2 SATA SSD Upgrade - YouTube
Lenovo ThinkPad T440 m.2 SSD and 2.5" SSD Install (how to + test run) - YouTube
Amazon.com: KingSpec M.2 SATA SSD, 512GB 2242 SATA III 6Gbps Internal M.2 SSD, Ultra-Slim NGFF State Drive for Desktop/Laptop/Notebook (2242, 512GB) : Electronics