how to delete event in FCpx

First of all, the best way to reclaim space and that you can do at any time with no fear of losing data: delete GENERATED files.

Select the library itself in the browser sidebar and do File->Delete Generated Library Files...

check all the boxes.

Quit FCP and see how much your library has shrinked in size. I bet about 90% or more...

Luis’ reply OSs where to start. If you really want to delete events or project, select them and puts Cmd-delete. You cannot delete all the events. The library has to have one.