Hi
You may have to do a re install of Windows from scratch especially if the M2 drive is smaller than the hard drive or smaller than the used space on the hard drive
If you run disk clean up, empty recycle bin, empty restore points etc you may recover a lot of space
but few programs for migrating Windows C: partition will go to a smaller drive
If your hard drive has a C: & D: drive and the C: partition can be cleaned up, size shrunk to same size as the M2 drive using something like gparted (bootable linux cd).
Then you can migrate the windows partition to the M2 drive using Acronis (often given for free by SSD & HD manufacturers.)
Each Windows hard disk has a identification number embeded in MBR, Windows and anti virus...