Did some searching around, and found there is supposedly a method to convert disk from mbr to gpt without reinstalling windows, through command prompt. But then I get message "Virtual disk service error: The operation is not allowed on a disk that contains a pagefile volume. " which I am seeing means it cannot be done on an occupied disk? Which is it? Seems like contradictory statements.
Can I just nuke my C: drive anyways? Planning on fresh install anyways to fix some problems, though I'd still need to figure this UEFI boot issue but I hope that would make this process easier somehow.