I created a site template from one of my sites, and now I want to delete it, but I can't find where to do it.
I have looked everywhere :(
I'm using SharePoint Foundation 2010.
In the settings page for the site collection that contains the site that you saved as a template, select the "Solutions" option under "Galleries" - there you will see a list of the solutions that have been added to that site collection. In SharePoint 2010 site templates are saved as solutions in the site collection and have to be activated there before they can be used. You will have to deactivate the solution here before you can delete it.
If you do not see the Solutions option under Galleries, make sure you are at the top level site by clicking "Go to top level site settings" under "Site Collection Administration".