Using the command line interface (CLI) : config : config system dns
 
config system dns
The config system dns command allows you to set the DNS server addresses.
Syntax
config system dns
set primary <dns_ip>
set secondary <dns_ip>
end
where:
Keywords and variables
Description
Default
primary <dns_ip>
Enter the primary DNS server IP address.
65.39.139.53
secondary <dns_ip>
Enter the secondary DNS IP server address.
65.39.139.63
Example
config system dns
set primary 65.39.139.53
set secondary 65.39.139.63
end
See also
show system dns