In $FBHOME/bin there's a tool named cvsreport.pl which manages (among other things) upgrading files from the main FotoBilder repository to your local $FBHOME directory.
The command you'll need to upgrade is:
$ cvsreport.pl -c -s
-c is short for --cvsonly (only copies from the cvs directory back to the live area, not vice-versa) and -s is short for --sync (which means actually do the copying, don't just print out what it would've done, which is the default without -s).
Using Tarballs: The easiest way to upgrading your installation is to grab the latest release of the FotoBilder codebase from http://www.picpix.com/download/code/ and put it in your $FBHOME directory. Then all you have to do is run the following command in a console:
Example 4.1. Tarball Upgrade
$ cd $FBHOME $ tar zxvf fotobilder-YYYYMMDDNN.tar.gz $ cvsreport.pl -c -s
Using CVS: Alternatively, if you opted to manage your installation through the use of CVS, you can run the --upgrade option in cvsreport.pl to sync your $FBHOME/cvs directory.