When you run apt-get upgradeit updates all installed packages on your system.
It is perfectly safe (unless you cut it off before it finishes) as all packages are from the repos (you should only install one's you trust) and are (probably) well tested before uploading.

The only small risk is a risk of bugs within the packages there self, but this could happen to any thing on any OS that was upgraded as bugs are common in any software and come and go based on version.

Should you upgrade ? Well thats up to you, I would say yes, if you don't like upgrade use the application-updater app, same thing no output to make you worried.

Here is some documentation for apt so you can find out more

Is apt-get upgrade a dangerous command?
Hi I have a closed domain that I can not add any new utility/software and I would like to set the same resolution to all the computers but have found there no good way using GPO is there a another way? Hopefully using VBS. I have read about changing the regestriy keys but will it work for different computers with different hardware? Is there any other option?
