matt@ubuntu:~$ sudo swapoff /dev/ubuntu-vg/swap_1; sudo lvreduce -L -4500M; sudo lvextend -L +100%FREE /dev/ubuntu-vg/root; sudo swapon
swapoff: /dev/ubuntu-vg/swap_1: swapoff failed: Invalid argument
  Please provide the logical volume name
  Run `lvreduce --help' for more information.
  Invalid argument for --size: +100%FREE
  Error during parsing of command line.

Usage:
 swapon [options] [<spec>]

Options:
 -a, --all              enable all swaps from /etc/fstab
 -d, --discard          discard freed pages before they are reused
 -e, --ifexists         silently skip devices that do not exis
 -f, --fixpgsz          reinitialise the swap space if necessary
 -h, --help             display help and exit
 -p, --priority <prio>  specify the priority of the swap device.
 -s, --summary          display summary about used swap devices and exit
 -v, --verbose          verbose mode
 -V, --version          display version and exit

The <spec> parameter:
 -L <label>             LABEL of device to be used
 -U <uuid>              UUID of device to be used
 LABEL=<label>          LABEL of device to be used
 UUID=<uuid>            UUID of device to be used
 <device>               name of device to be used
 <file>                 name of file to be used