Windows 10 Creators Update v1703 introduces a new MBR2GPT Disk Conversion Tool using which you can safely and non-destructively convert a Windows 10 computer from legacy BIOS to UEFI disk partitioning, as well as automate the conversion as part of your in-place upgrade process from Windows 7 to Windows 10. Moreover, unlike Wipe & Load methods, all of this can be achieved without having to move your data off the disk.
MBR2GPT Disk Conversion Tool
MBR2GPT.exe, located in the System32 folder, is a command line tool that will help you convert a disk from Master Boot Record (MBR) to GUID Partition Table (GPT) partition style without modifying or deleting data on the disk. You can run the tool from Windows PE (Windows Preinstallation Environment) command prompt, as well from the Windows 10 OS.
Using MBR2GPT.exe you can convert any attached MBR-formatted disk to GPT, including the system disk, within the Windows PE environment as well as withing the operating system. You can also use the tool to convert an MBR disk with BitLocker-encrypted volumes.
Operating system disks running Windows 10 v1507, v1511, and v1607 can also be converted, provided you are running it from Windows 10 v1703 and perform an offline conversion.
However, offline conversion of system disks with earlier versions of Windows installed, such as Windows 7, Windows 8 and Windows 8.1 are not officially supported – you will have to upgrade to Windows 10 first, then perform the MBR to GPT conversion.
You can read all about this new MBR2GPT Disk Conversion Tool, including the syntax to be used here at Microsoft.