Removing Ubuntu

I installed Ubuntu a few months ago on a whim. I now need the space back from my hard drive, and am trying to uninstall it. However, when I uninstall it, it leaves GRUB behind. From the guide, it says to get rid of GRUB in the installation, one should insert the OS installation disks and from there clear the MBR.

I bought my laptop from HP, and it did not come with Windows installation disks. How can I completely uninstall Ubuntu and get rid of the GRUB menu whenever I start up my computer?

Thanks for any help.