If you want to change the default host name "rafaela", log in as super user and edit the file: /etc/sysctl.conf with your favorite editor. By default, this is in line 9:
kernel.hostname = rafaela
All you have to do is to change the variable's value with your preferred name.
If you want to edit your hostname for the current session only, please type in your terminal:
# hostname new_name