I installed with NTFS and legacy bios, how hard to change?

[KYHI]

kyhi, I see our first respective posts in here were at the same time. Anyway, OP can use any number of free or fee partition backup/restore programs; as you said earlier, if he only image-backs the C-partition, he can restore OS onto the GPT'd C-drive later. I'm wondering if he also made a Ddrive partition for all his created and downloaded data, audio, visual, pics, etc. If so, that partition can be left alone, correct? He better image-back that Ddrive also, just in case the OS decides to format the whole disk.

You trying to throw a kicker in the mix I see,, As I seen he made not mention of a Data partition.. But yes he needs to back that up too..

If you check out Special edition in my sig below, it is a USB bootable windows 8.1 recovery enviroment

 

[KYHI]

most people disable secureboot anyway.. and GPT or MBR they are just two different partition structures..

BUT, the choice is yours.. And I can only offer advice