For anyone else wondering: This laptop (m6-w103dx) does not have an m2 slot. It only has a 2.5" SATA bay. I replaced the built-in HDD (Toshiba) with a Crucial MX500 and it works perfectly. Pair this guide with the RAM upgrade one by the same author (it supports up to 16 GB, two 8 GB sticks) and you have yourself a much faster laptop.

Great tutorial! The only things that weren't mentioned are the fact that you have to detach the little metal wires from the Wi-Fi card in the top-right of the motherboard, and you also have to take out the audio jack if you want to lay the motherboard upside down. Otherwise, this was exactly what I was looking for. Thanks!