Do you want to format drive or just remove windows?
if hdd is in pc,
to format drive -
go to settings/update & security/recovery
under advanced startup, click restart now
this loads windows into a blue menu
Pick troubleshoot
Pick advanced
Pick Command Prompt
Type diskpart and press enter
Type list disk and press enter
This will show the list of drives currently attached to PC, make note of the drive number of the drive you want to wipe
If Disk 1 is the drive you want to clear, type select 1) and press enter. A message will confirm it is selected
Warning: Diskpart Erase/Clean will permanently erase/destroy all data on the selected drive. Please be certain that you are erasing the correct disk.
Once you sure its right disk, type Clean and press enter
The Command Prompt window will display the message "DiskPart succeeded in cleaning the disk". Close out of the Command Prompt window by clicking the red X in the upper right hand corner.
just remove windows
go to old install and rename the windows folder as windows.old
run disk cleanup on the old drive
choose clean up system files
this will let you select a choice called "Old windows installs"
that will remove windows but the drive will still have a boot partition on it. Only real way to remove it is format drive