One cannot alter the layout of a disk if any of the disk's partitions is mounted.
You will have to boot from your install medium in "Try Ubuntu" mode, or from a USB stick with a system on it.
It looks like you are using an extended partition (an old trick to fool old DOS systems).
Run gparted, shrink the extended partition to move the free space from the extended partition to real free space and expand your "Part 5". Or, if you want to expand your "System partition", omit the "shrink the extended partition" step.