Making A Partition with Gparted - Unmount?
Solution 1:
You cannot unmount a partition while you are using it. The way to do it is to boot from a live CD or USB drive, and run gparted from there. Then you will usually be able to resize any partitions on your hard drive.
The original Ubuntu disk will work, as will specialized utility disks like gparted magic, but all of them simply use gparted to do the work.
Solution 2:
You cannot unmount the file system that you are booted into currently. What you should do is to boot into Ubuntu live and launch gparted from there. Since it is live, none of your partitions will be mounted and you can resize any partition according to your whim.
Solution 3:
After booting from a LiveCD or LiveUSB, then run Gparted; to unmount the extended partition, FIRST turn off the swap partition (part of extended partition) by right clicking on swap and selecting "swapoff". This should unmount the extended partition at the same time. Was having this problem booting from a LiveUSB, couldn't unmount the extended partition; puzzled, then by accident discovered that unmounting the swap partition would unmount both. After that, was able to resize as I wanted. Hope this helps.