You can do all that on the web gui, find out the ip address of the NAS and configure it on your browser.
When first powered on, during the initial boot sequence, the DNS-321 will wait to be assigned an IP address via DHCP.
If it does not receive a DHCP assigned IP address, by default it will have a self-assigned IP address of 192.168.0.32
If it's already assigned a static IP, I didn't see a mechanism to reset that ip without first logging into the device.