Newer PCs normally allows the user to choose between a bios (legacy) or UEFI. However when you switch from Windows 7 to Windows 10 you normally do not use UEFI and stick on the old legacy bios.
The reason why you wish to change to UEFI is that its more secure and offers different additional features which a normal legacy BIOS isn´t offering. On top of that the startup is often faster.
Check if your PC uses UEFI or BIOS:
To check what your current Windows OS is using you can use the "System Information". Inside the System Summary you will find the section "BIOS Mode" which will show if the legacy BIOS or UEFI is used.
Note: Before you change the Partition Style from Master Boot Record (MBR) to GUID Partition Table (GPT) as outlined below make sure you can switch to UEFI in the bios, otherwise you can no longer boot Windows!
Change from legacy BIOS to UEFI:
To change from the legacy BIOS to UEFI you need to change the Partition Style from Master Boot Record (MBR) to GUID Partition Table (GPT). Performing this step with Windows 10 is quite easy (but required an Admin Account):
01.) Open Settings
02.) Click on Update & Security
03.) Click on Recovery
04.) Under the "Advanced startup" section, click the Restart now button
05.) Click the Troubleshoot option
06.) Click on Advanced options
07.) Click the Command Prompt option
08.) Select your administrator account and sign in with your credentials (if applicable)
09.) Type the following command to validate that the drive meets the requirements and press enter
10.) Type the following command to convert the drive from MBR to GPT and press Enter
11.) Enter Exit or close the windows
12.) Click the Turn off your PC option
13.) Now several background options will be performed. The environment will create the EFI system partitions (ESP) and the UEFI boot files and GPT components will be added to the partition. Then the Boot Configuration Data (BDC) and the previous drive letter will be added to the drive.
14.) Make sure that you change the boot option from the legacy bios to UEFI otherwiese you will not be able to boot!