Here's how to replace (swap) and existing panorama with a new one, without having to recreate all the metadata.
1. Upload a new pano. Name it something obvious e.g. "the updated pano"
2. Edit the existing pano.
3. Go to the 3rd tab "other"
4. Scroll down to "swap image" and find "the updated pano" on that list.
5. Click save.
Your panorama is now replaced. Be sure to go and delete "the updated pano" (which now has the original pano - they've been swapped) so you don't get confused later on.
Keep in mind: Once you swap a panorama, it will have to be reviewed again by our review team.