So, I created an image in Web Image Studio, exported it as a PNG and then loaded it as an image in VSD. Then, not fully satisfied with it, I went back to WIS and altered the image and then exported it giving the file the same name (essentially overwriting it). Then, back in VSD, I wanted to update the image with the new file, but I couldn't find a way. I've got the image all nicely aligned, so I really don't want to delete it and then insert the new image and then get it all aligned again -- but that appears to be the only way!
You can do this with a background image, but not with an <img /> image.
You have to delete the image and re-add it back to VSD. That is the only way.