Edit: [Solved]
Auto-pack must be disabled (file - external data - unpack into blend files - disable auto pack), then Alt+R in image viewer to refresh… I still wish it was automatic 
If I have a .PNG material on an object and I’m viewing it in texture/material mode, how do I get it to automatically update when it’s edited externally? Currently I have to go into the material, browse my harddrive and find the file again manually and re-add it.
Is this possible? I recall in older versions there was a refresh button, but there’s nothing now. I’m hoping to have this automatic so I can save in photoshop, tab over to blender and the change is already made.