According to Davis.
To move the weatherlink data from your old PC use Windows Explorer to find and look in the Weatherlink installation folder. This WeatherLink folder is typically installed at the root (c:) or under the program files directory (c:Program Files). There will be a folder named after the name you chose for your station in WeatherLink (e.g. C:weatherlinkbrettsWX). Copy this entire folder, named after you station, and copy it to the new Weatherlink folder on your new PC. You can then open that station on the new PC and all the data should be there.
Alternatively, you can move only the individual data files. After creating a new station on the new PC using WeatherLink, copy only the old data files (not the whole folder as above) and place them in the “station name” folder on the new PC. The data files will have a .wlk extension and will be named by year and month (e.g. 2011-09.wlk is Sept. 2011 data).