How to delete all content from an album in Photos app?

I have loads of photos, I need to delete a lot.

Good thing is they are already organized in different albums. So I could delete those albums AND their content and be done.

Problem: Deleting an album does NOT delete the photos and videos, it only deletes the digital folder that grouped them. So if I do that, I don't even know how to find those related photos anymore.

I need to be able to delete a few albums that have hundreds of photos, how should I go about doing that?