This will delete all update history. I don't think its possible to delete update history selectively.
Go to Start menu> All Programs> Accessories.
Right-click on the "command prompt"> Run as Administrator.
Type this command:
net stop wuauserv
Press enter And validate.
Wait until a confirmation says the service has been stopped.
Now, give this command in the command prompt:
The service will relaunch automatically at next reboot.