The method to removing the meta name generator tag for Joomla varies between versions. On Joomla 2.5 you can simply add this code to your index.php file in your template.
The main advantage of editing the template code instead of installing a plugin is less overhead.
The fewer plugins you have, the faster your site will be, and queries add up fast.
Put it just after the line //no direct access.
This method will vary greatly on what template you are using and from what company.
For example YooThemes has a different template structure then RocketThemes.
You will have to noodle around a bit yourself in order to do this.