Switch to event with this button and then try delete
If this don't work, then it means ID of event was changed with some text editor. Therefore you need to open that map with text editor (recommended Notepad++), find mismatching ID, and change it value to something low (any number between 1 - 10), reopen project and then try to remove.
I think you should follow the build-in tutorials to learn the basics of maps and events before you continue.
because if you can't see the difference or don't even understand what an event is, then most likely you are missing a lot of the other things about the maker as well.
There are simply too many options in the makers to learn them by doing, you'll need a guide to get the basics. You can also follow the link to the starting point in my signature to get those.
Coding class: Python