Convert MBR to GPT - Without any OS

You should be able to do this with a live distro of GParted I believe.

This is a fairly generic tool which allows a number of operations to be performed on drives whilst booted up from a USB stick or CD-ROM

This is easy, when you go through installation guide, you can at any time press Shift+F10 - the command prompt will show up.

Then write Diskpart, then List Disk. You see there a list of your disks, then select the one you want to convert.

Select disk 0 (if you want to install on the first disk, for an example). Clean it with Clean, and convert into GPT Convert GPT. Enjoy

Unluckily I wanna MBR and got GPT :/