Gparted has a little key icon on my Ubuntu partition so I can not resize it

How can I make separate partition (to install windows 7) using ubuntu. I tried to use Gparted but there is a little key icon on my ubuntu partition therefore i cant make a new partition.

That key icon indicates that the partition you are trying to modify is currently under use. In order to modify that/those partition/s you have to boot up from a live CD. Then you will be able to modify those partitions. But, be sure to backup your data as it can lead to data loss. But this case is very rare.

If you've booted from a live USB/CD and still see the key icon, check if you have mounted the partition. That could have easily been done if you clicked one of the drive icons from the desktop to check to see what was on the drives.

Unmount those drives by rick clicking on them and choosing "Unmount".