You can use Disk Cleanup to remove the older system restore
points but I don't think you can remove individual restore
points.
You can also go to to My Computer, right click Properties,
choose System Restore then turn off the System Restore.
That will remove ALL system restore points. I would
suggest if you do this that you immediately reboot then
go back to systen restore and turn it back on. It might
be good idea to set a restore point also.