Unfortunately our admin panel does not have such option for now. But, there is a workaround:
You need to replace /xml folder by the one you have in your template installation package. Just to clarify - you should upload /xml folder including all files&folders inside it from the original template and replace the existing ones on the server. Mentioned /xml folder is located in your template root directory.
Just a reminder - you can use "Undo" and "Redo" buttons to go through your changes history. You can also use hot keys for that: Ctrl + Z for "Undo" and Ctrl + Y for "Redo" operations:
Or use "Revert changes" button. It reverts all the changes you have made since the last time you've saved the changes: