I can't find the "upload picture" button to edit work thumbnails

[haydn_enjoyer]

Hi =) I've recently updated an edition of mine and want to update the thumbnail as well. i've looked around the guides and forums to see if i can find the answer on my own, but nobody seems to mention exactly where to find the "upload picture" button, or they have and i'm just unable to find it myself for whatever reason. sometimes i'm extremely oblivious about random things, so i'm not discarding that. could someone tell me which page i can find the "upload picture" button on? is it the work page? the file page you get to by clicking the hashed number? the "upload new version of this file page"? and considering i've looked on all these to no avail, if you could attach a screenshot with a big red circle or something that'd be amazing. i use the regular not-clara not-wiki skin. thank you!