I ran sudo apt-get update an sudo apt-get upgrade.
I got the following message
The following packages have been kept back: libraspberrypi-bin libraspberrypi-dev libraspberrypi-doc libraspberrypi0 lxpanel lxpanel-data nuscratch pypy-upstream raspberrypi-bootloader raspberrypi-ui-mods
I'm not sure, what this could mean. Why aren'r those packages kept back instead of being installes/updated?