A not in use template may not a big thing for most of us. However it is better to delete it because some templates could be coded in a way that could pose risks to your site, even they are not in use. There is an option to delete templates from the Template Manager, however this will only delete the template style. For most users that try that step, the following error is given:
Cannot delete last style of a template
To delete a Joomla! 2.5 template you will need to follow the steps below and use the
Extension Manager instead.
I tried to post this many times but can't because of internet connection. Is it possible to find a cheap internet locally?
Have fun!