To upgrade from CE4 to Backlight:
Take note, this process will only migrate albums created by TTG Publisher, our Publish Services plugin for Lightroom. Your albums and album sets will be assigned the default templates for Backlight 2. You will need to redo your design, pages, etc.
Galleries exported from Lightroom's Web module cannot be upgraded; you will need to publish such albums anew using Backlight 2.