It should be perfectly safe to use any Windows operating system on the laptop. But always make a disk image of the way the system is now before doing a drastic move like that. Make a disk image to a USB drive or something similar in case you want to go back to Win8.
In fact, what I would do after that, is do a restore to factory condition. Then make another disk image of that in case you want to return it to as bought condition for resale. Or to send it in for warranty work.