I’ve been using Forge for the past few months. Just two weeks ago, I am unable to update the token images. I would upload, save and close. But no changes.
The only way would work is if I move the token onto the mat and update the played token’s image. It is quite annoying since I am unable to update the original token and keep updating it every time.
The way Foundry works is that each actor as a “Prototype Token”, and that’s what you need to update. Open the actor’s sheet then click on “Prototype token” from the title bar, then change the icon for that prototype token. Save, and that should do it.
You could also select a token and click the “Assign token” button to assign the currently selected one as the new prototype.
I hope that helps