Board Thread:Questions and Answers/@comment-32098919-20170524171334/@comment-979971-20170524181745

Click the image you want to replace, then click the name of the file (e.g. Volume 29.jpg).

It'll take you to a page like.

Click the arrow beside the Edit button and then Replace. You could upload the new file there and it'll update on all pages.

Edit: Actually, it looks like that won't work since the ones currently uploaded are all .jpg and yours are .png.