Let's consider an Ubuntu 15.04 installation which takes the whole HD space:
Is it possible to shrink either /dev/sda2 or /dev/sda5 in order to get free space (with a view to install a more recent Ubuntu version and make it bootable)?
I tried with Ubuntu Disks utility and Gparted to no avail.
Because you chose to install Ubuntu using the LVM disk structure method, you can't use gparted to make modifications to your disk. Install system-config-lvm and use this GUI tool to review/change your disk volumes.
In terminal...
sudo apt-get update
sudo apt-get install system-config-lvm
Start it from the Unity dash by typing lvm into the search box.
See https://wiki.ubuntu.com/Lvm for basic help. You can also search https://help.ubuntu.com for "system-config-lvm" and find a lot more detailed help.
