Turning off system protection for a disk deletes all restore points for that disk. You can't restore the disk using restore points until you turn system protection on again and a new restore point is created. Turning off system protection also deletes any previous versions of files that were saved for that disk. Previous versions are copies of files and folders that Windows automatically saves with restore points. For more information about previous versions, see Previous versions of files: frequently asked questions.
Open System by clicking the Start button , right-clicking Computer, and then clicking Properties.
In the left pane, click System protection. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
Under Protection Settings, click the disk, and then click Configure.
Click Turn off system protection, click OK, and then click OK again.
http://windows.microsoft.com/en-US/windows7/Turn-System-Restore-on-or-off