Q:  How to uninstall GRUB from my hard disk drive?

A:  There is no concept uninstall in boot loaders, because if you uninstall a boot loader, an unbootable machine would simply remain. So all you need to do is overwrite another boot loader you like to your disk, that is, install the boot loader without uninstalling GRUB.

For example, if you want to install the boot loader for Windows, just run FDISK /MBR on Windows. If you want to install LILO (I can't imagine why you want to do such a thing, though), run /sbin/lilo on GNU/Linux.