Hello there,
@Katka Kalinova. Welcome to iMore.
Are you wanting to delete multiple images from a single iMessage? If so here's what I did and it worked.
I went to a message with a friend yesterday that had some camera lens photos. Two photos to be exact.
When I touch and hold on the first image, I get this:
I have the option to like/dislike/etc the image at the top, but them I also have a menu at the bottom. If I select More, I get this:
I now have the option to select both photos from the message, then click the trash can icon, confirm you want to delete both photos from the message, and POOF the images are gone but the message is still there.
Hope this helps. If it did, please like this reply.