On the original layout, select all objects and delete them.
On the new layout, select all objects and copy them to the clipboard.
Then go to the original layout and paste.
There are, of course other complications to consider if the theme is different or you have differently sized layout parts, but since FileMaker references layouts in scripts, etc by an ID number, it's one way to update a layout.
I frequently duplicate an existing layout, modify and test it until I'm satisfied that the changes that I've made will work, then I do the above copy/paste operation to update the layout that the users actually interact with.
Great to confirm that way is the only way...thanks. Wow I thought there would be a more internal way this could happen. I am going to look into making a feature request for this. I would like to see something that could also swap the way that FileMaker changes the name. When it changes name... its updating is great, a swap option would be even cooler. Thanks
Many times it's not necessary. It's often quite easy just to update a few navigation scripts to specify the new layout instead of the original.
3rd party tools such as base elements or Inspector Pro can make it pretty easy to find every reference to a given layout in any of your scripts, buttons, etc.
I see... Thanks so much!