the best way to convert them is with a fresh install as there are ways to convert them but its not reliable.
easier to just swap the boot method and bios type and fresh install on whatever you installing onto.
follow these instructions for clean boot: http://www.tenforums.com/tutorials/1950-windows-10-clean-install.html
Thank you for messaging. No i am not installing windows on the 5tb as i have that on an SSD dedicated entirely for windows. This 5tb will serve as my main storage for all other activity. Kindly please tell me if following this method would help if i dont want a clean install: