I have developed a custom (private) theme, I plan to use on multiple installations. I would like to have the theme installed on installation (A) and whenever there is a change made to it on (A), update it on installations (B), (C),… by simply “updating” it inside the dashboard (not uploading the updated version).

Sorry, I have no idea how to do that and maybe I asked Google the wrong questions, but I have not found a solution there either?

And the same for plugins? Where must plugins be stored so that updates are recognized wherever the plugins are installed. Thanks for your patience.

Vlo