How to remove a picture from Slide Show?

Select them all, and then use "File>New Album with Selection" to create your own Album. Then you can remove a picture from that album with Delete. (NOT Command-Delete. That would remove the picture from the entire Library!) Then you can use "File>Create>Slideshow" to make your own TripShow the way you want it.

Click on them in the bottom tray and hit the Delete key. Like this: