I had considerable trouble changing the IP address on a new 1820. I set my PC up with a static IP of 192.168.1.21 and logged into the switch. I changed the switch address to 192.168.3.249 to match our network. Pressed "Apply" and of course the screen became unresponsive because of the change in the IP. I unplugged the switch and moved it to it's new location. Started it up and I could not log into the switch.
After several attempts I figured out why. Hitting "Apply" changes the IP address immediately, but does not save the configuration. I needed to change the IP address on my setup PC, and log back in to the switch and Save the configuration before unplugging the switch.
Hope this helps the next person trying to do this.