matt@ubuntu:~$ sudo lvreduce -L -4500M ubuntu-vg/swap_1 &&  sudo lvextend -L +100%FREE ubuntu-vg/root
  WARNING: Reducing active logical volume to 5.57 GiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce swap_1? [y/n]: y
  Reducing logical volume swap_1 to 5.57 GiB
  Logical volume swap_1 successfully resized
  Invalid argument for --size: +100%FREE
  Error during parsing of command line.