There are many reasons to convert your computer from the traditional BIOS to the newer UEFI standard if your hardware supports it. You will notice slightly faster power on times and support for new security capabilities such as Secure Boot, Credential Guard, and Device Guard when using UEFI. Traditionally the only way to switch from BIOS to UEFI required a complete rebuild of your PC. But with the Windows 10 Creator Update or newer, there is a useful command line utility that will save you a ton of time.
There are typically two steps to converting your PC to use UEFI boot compared to the legacy BIOS option. First, the hard drive must be converted from an MBR (Master boot record) partition table structure over to a GPT (Globally unique identifier) partition table structure. Second, UEFI must be turned on in your motherboard settings.
How to Converting Your PC From Legacy BIOS to UEFI Bios Using CMD :
1. Open an command prompt.
2. Type the command below into the elevated command prompt, and press Enter.
mbr2gpt /convert /allowfullOS
3. When the conversion has successfully completed, you will need to boot to UEFI firmware settings, and switch the firmware to boot to UEFI mode instead of Legacy BIOS (CSM).
If the validation failed, the drive may not be compatible for a number of reasons, most likely, there is not enough space to create the new GPT partition table. Your only option at this point is a full rebuild of Windows 10.