I just changed my OS drive from a 64GB M4 to a 128GB Samsung 840. I used Acronis, in windows 7, and it worked without any issue. You set it up in the application, Acronis shuts down the system and reboots in its own stripped OS and clones the drives. Once it's done, it shuts down, you pull the old drive and/or change boot priority in BIOS, and you're off and running. I can't remember if the Acronis disc needs to be in an optical drive or not. Either way, it was pretty simple.