There is a site for templates.
Unfortunately there is no way to delete a template from inside the game. You can navigate to your game folder/saved_objects/stonehearth/building_templates. Every template has a json file (blueprint) and a png file (image). Deleting both deletes the template.
I don’t recommend renaming the templates in this way, though. The name of the building is saved in json file, so changing file names can throw some errors your way. If you want to rename the template, better resave it in the game, then delete the old version manually.
PS. I guess renaming and deleting should be added to the game itself. It doesn’t seem a difficult feature to implement and can make the process less… manual.