Source: https://support.google.com/earth/answer/176177?hl=en
Windows Vista and Windows 7 Users:
- Make sure that Google Earth Pro is closed.
- Click Start > Start Search.
- In the Start Search dialog box, type in C:\Users\%username%\AppData\%Local or LocalLow\Google\GoogleEarth and click OK. Alternatively, you can navigate to this folder manually by first double clicking the Computer icon on your desktop and navigating through the same folder structure .
- Windows Explorer should now open up a GoogleEarth folder showing you several Google Earth Pro Files, including: My Style Templates Folder, myplaces.kml, myplaces.backup.kml, and myplaces.kml.tmp.
- Make a copy of all of the files in the GoogleEarth folder, and save them in a different location, such as a folder on your desktop.
- Delete everything in the GoogleEarth folder (make sure you’ve backed everything up first!)
- Close the GoogleEarth folder and open Google Earth.
- After logging in to the server, Google Earth Pro should create new files in the GoogleEarth folder to replace the ones you’ve moved out.