What is the GRUB Bootloader?
As basic as it sounds, the GRUB loader is used with Linux distributions such as Ubuntu in order to allow you to switch between different hard drive partitions that have different operating systems installed. Partitioning is the system of separating space on a hard drive for different media or operating systems. You can even partition your hard drive using Disk Management in Windows in order to store music, for example.
How to restore Windows MBR?
If you intend on installing Ubuntu and dual-boot between Ubuntu and Windows, the GRUB bootloader will be installed. To remove the Ubuntu GRUB bootloader, you will need to reinstall the Windows MBR which can be done with a Windows installation disc. Follow the instructions on Microsoft’s Support page to do this, but when it tells you to type and execute bootrec.exe, type: bootrex.exe /fixmbr. This will restore the Windows MBR. Now you will be able to delete the Ubuntu partition via Windows “Disk Management” utility (by right-clicking on Computer from the Start menu and selecting Manage).