Repartitioning after LVM partitioning

I installed Ubuntu 16.04 using LVM method. Now while trying to re-partition HDD using Gparted, I saw that my HDD present situation is like this : LVM is using the entire part of extended space. (Also both of them are locked ? why ? I did not lock those with any password or anything!!)

I searched through this forum and found another similar question LVM Hard disk partitioning after Ubuntu installation and did as pas4080 said.

While defragmenting with sudo e4defrag /mnt

I got the result

Success:            [ 140820/243617 ]
Failure:            [ 102797/243617 ] 

though each of the processes showed to be 'ok'

2nd step showed : $ umount /dev/ubuntu-vg/root

umount: /mnt: umount failed: Operation not permitted

Now I don't know what the faliure was or why umount was not permitted. Can anybody help me here?

EDIT : as suggested by oldfred

sudo umount /dev/vg_ubuntu/lv_root
[sudo] password for alpha: 
umount: /dev/vg_ubuntu/lv_root: mountpoint not found