Cant delete attachments to messages

ios10 added some cool attachment options to messages, but my son is sending me dozens of things, and they are taking up space, and I can't delete them. I followed the instructions online, but when I tap and hold on the attachment, the screen does not display a 'More' prompt. The top left of the screen says 'Done", the bottom left has a box with an arrow on top, the bottom right has a hamburger menu, when I click on these and select More, there is no option to delete. Please help. Thank you.

Pressing and holding the attachment provides me with the attachment option screen. I can either add an emotion to that attachment or I have the options below it.



Selecting more gives me the option to select individual messages I'd like to remove.



Once selected just hit the trash can at the bottom.

Hope this helps!!