If the covers share the same extension, then replace the original, don't upload it separately. Thumbs already work fine.
Topic on User talk:AlphaYellow
Yes, I tried it before, but the new versions never show up in the articles somehow, unless I change the file entirely
Oh sorry, they need to have the same extension as the original one?
> Yes, I tried it before, but the new versions never show up in the articles somehow, unless I change the file entirely
You need to purge the cache (More->Purge Cache), sometimes several times.
> Oh sorry, they need to have the same extension as the original one?
Yes. If it's JPG image it can't be replaced by PNG image and vice versa, but in this case both were PNG so it's possible.
If and only if the cover shares the same extension as the original, yes. Also, the reason why covers (and images in general) which get updated don't immediately show up on the pages they're on is 1) the wiki has to process the new image, 2) your browser needs to update or clear its cache of the affected pages (Control+F5 is the usual key combination to do this), and 3) the page's internal cache may need to be forcibly cleared by going to the More dropdown menu on the affected wiki articles and selecting Purge cache from the list of issues.
Thanks to both of you, I'll keep that in mind. I've edited and created many articles, but never really touched the covers much before, so that's why I was a bit confused haha.