Shutdown slave

You can open a telnet session across the HA links.

From master CLI:

"exec ha manage ?"

this will show you the unit IDs available. In a 2-unit cluster, 0 or 1.

for example,

"exec ha man 0"

Now you are connected to the slave, and have to log in.

Once you're logged in, type "exec reboot" and "y" to confirm.

I would stop port monitoring just before this, and restore the setting after the reboot. This avoids a small interruption in the service of the master unit.