To remove the Ubuntu boot loader, you have to boot from the Windows 7 Installation Disk (or a bootable USB drive) and click on the
Repair your computer link in the bottom left corner. After this, select your Windows 7 installation and click
Next, then select
Command prompt. After this, type the following commands:
This will restore the Windows 7 boot loader and remove Ubuntu from startup.
To completely remove the Ubuntu installation, you can remove the partitions that Ubuntu used with Disk Management. To open it, open the start menu and type
diskmgmt.msc and hit enter. This will show all the partitions on your disks, and you can remove the ones that were used by Ubuntu (they have no filesystem recognized) and create new partitions for Windows if necessary (or extend the current partitions). Here's a small tutorial on Disk Management.