Hello Sam, how are you?
I understand that you would like to convert your installation from Legacy to UEFI, I suggest you check the thread below, but to be safe, always before taking any action, make a backup of the important files on your computer.
It is very detailed and will be able to assist you in this process.
https://answers.microsoft.com/en-us/windows/for...
When finished, enable safe boot and switch from Legacy to UEFI, and try updating again please..