You cannot edit the computers nickname from the PocketCloud Companion application. You can ONLY edit the nickname (on the device) with PocketCloud installed. Changing the nickname on the mobile device will not change the name of the computer it is actually connecting to, only its nickname that is displayed on your mobile device.
If you would like to edit the nickname on your mobile device, select Edit on the auto-discovered connection. After selecting Edit, you will be on the Connection Settings screen. On this screen, you can tap where it says Nickname, after doing that the Edit Nickname screen will show. From here you can edit the connections nickname (local only, this will not actually change the name of the computer you are connecting to).
If you wish to change the actual name of the computer you are connecting to, you must do it through that computers operating system.