It can end up very badly if you don't read what will be upgraded. If you do read and then install only what you need nothing bad will happen. But the problem is that most people after apt-get upgrade simply just press "y". That's why tis is a bad advice.
Anyhow, CSSU should appear in HAM, if not, refresh. And it can be installed that way, If it doesn't, check the details, it will show what is the problem.