How To remove Collection without deleting pictures?

To remove a collection without removing the photos:

RIght click on the collection name and ... well, you can figure it out from there.

Collections are just LISTS of images. Like writing a list of your albums/CDs. If you throw that list away you still have the actual album/CD.

You may have to first Remove all the image entries from the collection/LIST before you can delete, Remove, the Collection Name. Not sure I've never needed or wanted to remove a collection, as far as I can remember.

When you remove a collection, it doesn't remove the images because the images don;t really exist in the collection.

A collection is just a link to images in your catalogue (and your hard drive).

That's why when you remove a collection, Lightroom doesn't give you any warning dialogue box.