How to remove thumnails attachment from a thread?

Hi all, I've a small issue with the forum, few months ago I've opened a thread about an app I'm working on ( thread link ) and I attached some images of it. Today I've updated the thread with other info and I would like to remove those old images, but I cannot found a way to do that. Is it normal? should a moderator do it for me?

Thanks for the help!

(I tried searching about this kind of issue with the search feature, but it seems that I'm falled inside "Inception", I've only found thread in xda that talk about attachment in android apps :D kinda funny )