Note that https://instavideosdownloader.com no longer really works so I've switched to using https://ingramer.com/downloader/instagram/ as an alternative, I'll have to see about editing those original posts.
You can't edit posts that were imported from the old forum; best just make a new thread.
I use the Firefox element inspector to upload photos and videos from Instagram. It is the most practical if you know a little HTML, you can copy the URLs directly, without downloading anything. I also use the Firefox extension Instagram-guest, it removes the login window.
Instahighres.com is good. You just paste the entire source code into the website and it will spit out all the best quality versions of photos and videos from the post