How do I switch from Legacy BIOS to UEFI?

Hello everyone,
I recently had an issue with my Sony Vaio SVJ202A11L where the config files were corrupted and decided that a clean install of Windows 10 was the best option. My device was using UEFI at the time and from the UEFI firmware UI I set the boot order to external device then hard drive in order to boot Windows from a Flash Drive. The OS wouldn't boot, however, and so I set the BIOS mode to Legacy (per something I read randomly on the internet). Everything booted after that and after deleting the old hard drive partitions and creating new ones with a MBR format, windows installed itself no problem. However, I'd like to switch back to UEFI. I tried using Windows MBR2GPT.exe and... the partitions reformatted but then I restarted the computer and the Legacy BIOS could no longer read the hard drive and went looking for an external drive and screaming "No Operating System Found_". I then did the whole thing over and installed Windows once more. I don't know where to go from here. I've read article after article on how to resolve this issue but while I can format drives and partitions just fine, how on earth to I switch back to UEFI?

Hi are you willing to try just installing in uefi ? if so see if this video will help YouTube

kelsey said:

switch back to UEFI.

If you had done the above in the BIOS settings, the following would not have arisen.

kelsey said:

Legacy BIOS could no longer read the hard drive

kelsey said:

I tried using Windows MBR2GPT.exe

I used DiskPart, which might be simpler: Create Bootable USB Flash Drive to Install Windows 10

Brink said:

Hello Kelsey, and welcome to Ten Forums.

The tutorial below can help show you how to clean install Windows 10 with UEFI.

Clean Install Windows 10

Basically in the steps above:

1) Create a Windows 10 installation USB for UEFI.

2) Change your BIOS settings back to UEFI instead of Legacy BIOS (aka: CSM).

3) Boot from USB.

4) Clean install.

5) etc....

I wish I'd read something like your linked article before I began. Instead of switching of fast boot and secure boot I changed the BIOS to legacy. But maybe I wasn't clear in my question. My problem now lies in step 2. HOW do I change my BIOS settings to UEFI?? I can't find any BIOS UI of any sorts anywhere. And any F keys I press at startup or Del or Esc or even the Vaio Assist while the computer boots triggers Advanced Recovery which of course has no firmware settings options in Legacy. If you don't mind, what do

kelsey said:

HOW do I change my BIOS settings to UEFI??

Do you have a motherboard manual? If not, try resetting BIOS to the default, which should support UEFI.
Remove the CMOS battery and put it back after 30 seconds.

I don't have a manual. And I took as much of the computer's back apart as I could, but I couldn't find a CMOS battery. I found hard drive, RAM, and some other chips. No motherboard or even fan. The case of the computer doesn't come off easy and I opted out of ripping the whole thing apart for fear of damaging the large glass screen. Are there any other ways to reset the BIOS to default?

@f14tomcat
Thanks for trying, but this is no bueno. As I said in the beginning, I'm in legacy trying to get UEFI. So none of your suggestions will work. UEFI is the factory default. I don't know how to get back tho.