Change UEFI boot to legacy boot after installing windows 10?

@AnuSara199  changing the boot mode doesn't delete anything on your hard drive.  However, if you installed Windows while your system was in UEFI mode, then you won't be able to boot it anymore if you switch to Legacy later.  The reason is that Windows sets itself up differently on a system depending on whether it will be booted in Legacy or UEFI mode, including setting up different hidden partitions.  If you want to use Legacy boot, then you'd have to change that BEFORE you install Windows.  But realistically you shouldn't be using Legacy boot anymore anyway.  Windows 10 supports UEFI boot, and using UEFI also allows you to enable Secure Boot, which is a nice anti-rootkit protection.  Windows 10 will also no longer update itself on systems that support UEFI boot but are still configured for Legacy boot, and Intel has announced that starting in 2021, its CPUs won't even support Legacy boot anymore.  So why are you even trying to switch back to Legacy mode in the first place?  If you share more about what you're actually trying to achieve, there might be a better way to achieve it.  So even though there might be guides to convert a UEFI Windows installation to a Legacy Windows installation as @U2CAMEB4ME , that really wouldn't be a good idea. The much more common path at this point is to convert a Legacy installation to a UEFI installation if needed.