From the “Volume Manager” function you can add a disk volume to a new LV,
or increase the size of existing LVs (you cannot decrease LV size).

To set the needed LV size just use the scrollbar.

On the right side of it you will find a counter of available space.
This function can be also used to reserve disk space for swap, snapshots, system and replication.

Also if your system has a 4GB of SWAP, you can delete it to free some space.