Stopping a machine when connected through KALI
The Kali Linux instance and the PG machine can be closed by clicking the "X" on the upper right corner.
Note, switching between machines does not require closing the current Kali machine/PG machine. When you select a new machine, your current machine will be closed and the new machine you selected will be opened in the same Kali instance.
Stopping a machine when connected through VPN
The same command used to start a machine is used to stop a machine.
The command to stop is located on the far right of the lab machine row. Simply click the start/stop command button.