your can see your host name when you login with ssh

root@ubuntu:~#

you can type the command hostname to see your hostname that will give you ubunutu (in this case)
you can temporarily change it with typing hostname myserver

or if you want to change it permanetly you cant edit the file /etc/hostname and change ubuntu to myserver

you may also want to edit /etc/hosts and replace 127.0.0.1 ubuntu to 127.0.0.1 myserver

keep in mind these effects will only take place if you restart your server, but if you don't want to do that you can run this command to do so with out a restart:

/etc/init.d/hostname.sh start