Our problem ist that we cannot delete the "old" advanced actions (the action which come from the previous courses: one course was taken as a basis for many times and the action which were develop in this very course at the beginning now stay and cannot be deleted). Surely here is a screenshot.

if I open e. g. the action 010_02 it is empty (they all are empty, they even dont have a name in the fenster). but nevertheless you cannot delete it.

If the action still has a 'link' with an event, you cannot delete them.
Sighing, I never understood why so few people are using shared actions which have so many advantages over advanced actions: you can manage them in the Library, you'll see their usage like for any other asset. Reusing them in another project is so easy with external libraries. Copy/paste (for anything) is a very common work flow but based on my many years of experience (teaching software applications since end of 1980) I avoid it whenever possible. Same with reusing a project, why not use a custom Theme for design consistency?
The only way to get rid of those old actions is to create a new blank project with the same resolution (and use the same theme), and copy/paste (ugh, but that is one of the exceptions where I am using that) slides in bunches to that new project. Be careful with slides and objects that have attached actions, you should have to unlink them first which is a pain.....