Agree with the "if isn't broken etc." but I have to replace the graphics card and the new one I got needs UEFI.
Hopefully it isn't some card that uses a lot of memory or put the frame buffer above 4GB.
First you are going to need AOS 5.1 or newer. Simplest is to do a EUFI install, change to UEFI boot in the BIOS. You will need a UEFI partition, which Windows may have already created, otherwise about 256 MB FAT32 partition that will, if needed, be created during the install assuming you have the empty space. Can't remember if it needs to be a primary.
Then install AOS 5.1
Updating, IIRC, is not supported from a BIOS boot to UEFI though it is possible with work.