Technically yes, although depending on whether it's retail (purchased from a store or online) or OEM (shipped with the PC) will determine if you need to call Microsoft or not. However, in either case, yes you can.
My Computer
At a glance
Windows 10 Pro x64Intel Core i7 4790K @ 4.5GHz32GB DDR3Nvidia GeForce GTX970
thanks for the fast reply.
I just want to make sure, so I can register x64 retail version on a computer that had x32 retail version registered.(of course I would format my main hard drive and install x64 version
If you do decide at a later time to clean install from 32-bit to 64-bit, here's a lot of useful information that may prove useful in these tutorials linked below.