If yes.

1. Stop server ./vhserver stop

2. Backup ./vhserver backup

3.
https://docs.linuxgsm.com/steamcmd/branch
Following from instructions here, edit common.cfg inside your VM.
Location:
~/lgsm/config-lgsm/<your_server_name>/common.cfg
Changes:
branch="public-test"
betapassword="yesimadebackups"

4. ./vhserver update then once up ./vhserver start.

Hope this helps