Hello Tracey,
Its not possible to convert your install from MBR to GPT (easily) simply by making some changes in BIOS. The formatting on the disk has to be changed as well. To save your current install and OS, I would suggest using Macruim Reflect or Acronis True Image.
I have used Macrium for this several times, converting an MBR install to GPT so bitlocker could be enabled. This is a helpful article:
https://kb.macrium.com/KnowledgebaseArticle50151.aspxOne of the other benefits of Macrium is its automatic FixBoot utility that is built into the software. It moves and repairs what gets broken during the restore and takes out all of the guess work.. The easiest way to do this is to have a usb hard drive and a USB stick with your OS.
You partition the hard drive with a small winPE boot partition and a second large partition to store your back up image.
You boot into Macrium with the PE environment hard drive, run the program and back up your system disk (to the large partition). This way you have Macrium and your saved disk image in one location. Shutdown. Now you change your BIOS settings from Legacy to UEFI. Then use your USB stick with your OS to convert your system drive from MBR to GPT. You can use DISKPART for this. Now your system drive is wiped and formatted GPT. Boot into Macrium again. Restore your back up image. The program restores the MBR backup as GPT. Run the FixBoot Utility when complete and when you restart, you'll have your OS just as it was, but formatted GPT.
If you don't care about your install and have your data backed up... Just grab your install media, make changes to your BIOS, and install as UEFI. When you get to the point where you select your target disk for install, press shift+F10 which will open a command prompt... run DISKPART and format GPT. Now install your OS.
It looks more complicated than it is. Macrium has proven very reliable. Hope this helps.