If you really "just" upgrade (as you describe), your preferences and user data should stay untouched, even Windows has become capable of this nowadays. If you instead prefer to wipe all and fresh install, it is indeed needed to backup and restore all data you want to retain. Note that beta software is by definition unfinished, and third-party support (graphic drivers) may not be available or not in usual quality. Beta software is not intended for normal end users.
In any case, having backups is save:
Make sure you save the SketchUp installer that you want (only the current versions are downloadable at any time). Backup your SketchUp user data (plugins, components etc.):%(#000000)[%USERPROFILE%\Application Data\SketchUp\SketchUp 2015\SketchUp]
(In older versions this is in the program folder.) BackUp your SketchUp preferences from the registry (only if you feel comfortable using the registry)
Open "regedit", navigate to the hive " %(#000000)[HKEY_CURRENT_USER\Software\SketchUp\SketchUp 2015]" and Registry → Export it to a file.