SSH to your ESRS-VE appliance, and login as "root"
If you're using PuTTY; run the following so the boxes display correctly: export TERM=linux
Arrow down to "Network Devices", Tab across and arrow down to "Network Settings" and hit Return
Tab around to Overview then right arrow to "Hostname/DNS"
Tab down to the DNS section, and make your changes
Tab around to "OK" and hit return, or press F10.
Hope that helps!