Apple's Messages app offers one of the most convenient ways of having a text-based conversation with your contacts on iPhone and iPad, but messages aren't the only things you can send and receive. Apple's iMessage service enables all manner of files and attachments to be shared, such as photos, links, documents, audio messages, and more.

Files that are sent to you can of course be accessed directly from within a message thread, but you don't have to go scrolling through hundreds of messages to delete the files you've received. Apple also provides a way to see every file that has been sent to you in a chat thread in one easily accessible location, where you can remove them all in one fell swoop to free up space.

Launch the Messages app on your ‌iPhone‌ or ‌iPad‌.
Open a conversation, then tap the contact bubble(s) at the top of the screen.
From the menu that expands, tap the info button (the "i" icon) to view more information about the conversation.
Scroll down to the attachment sections, where you'll find all the files that have been sent to you in the course of the conversation. These sections are conveniently subdivided into file types, such as Photos and Documents. Tap See All to see all the files related to a category.
Tap Select at the top-right corner of the screen, then tap the files that you want to delete to select them.
Once you've made your selections, tap Delete in the bottom-right corner of the screen.
Tap Delete [number of files] Attachments to confirm.