The default hostname of the GuruPlug Server Plus is "guruplug-debian" or similar. I don't like it because I want to see my shares on my plugcomputer under a different name, like "plugserver".
To change the hostname, first edit the file /etc/hostname
$ vim /etc/hostname
There is only one name in the file. Overwrite the name with your desired hostname like "plugserver" and save the file. Now you have your new hostname.
One more step is required since it could cause some problems when allowing other users to use sudo-commands (like I used it here): there could be a error saying "unable to resolve host xyz" (where xyz is your hostname)
Take a look at the file /etc/hosts
$ vim /etc/hosts
It probably looks like this:
127.0.0.1 localhost 127.0.0.1 debian 127.0.0.1 guruplug-debian
Since you just changed the old hostname "guruplug-debian" to your new one "plugserver" or so, you also have to change the according entry in this file. The new file looks like this
127.0.0.1 localhost 127.0.0.1 debian 127.0.0.1 plugserver
save it, and you're done!