assuming you have an M.2 socket or are mounting the sm951 in a PCIe adaptor card, you can't "move" or copy the windows 8.1 to the new drive.
The sm951 does not have an OPROM (boot files) - you'll have to do a fresh install. Go to RamCity's web, they have complete installation directions - and consider yourself lucky - it took me 18+ hours of researching the web to get my windows 7 installed on a xp941. Below link is for both xp941 & the sm951
https://www.ramcity.com.au/blog/how-to-install-windows-8.1-on-the-samsung-xp941-ss/138296
actually you can clone your copy of win 8.1 if, and that's a big if, it was originally installed under UEFI or with a EFI boot file. I also discovered a "fred flintstone" clone method out of frustration, described here
http://www.tomshardware.co.uk/answers/id-2615594/installing-samsung-xp941-win-64x-boot-drive-fun.html
but your best bet is a fresh installation
and fyi, the sm951 is PCIe 3.0 x4 SSD - if your M.2 socket is not "Ultra 3" or PCIe 3.0 x4, to take full advantage of the sm951's capabilities, you'll want to go with a PCI adaptor expansion card like the addonics, if you have a PCI 3.0 expansion slot available - there are others out there, but a few are simply the addonics rebranded with a higher price. I've been running the addonics card and haven't had an issue, no drivers needed - $19 + shipping
http://www.addonics.com/products/adm2px4.php