User details, the quota of the different accounts (NICE, AFS,..) and other things can be changed at http://cra.cern.ch.
If your quota should be increased by more than 50 MB on your AFS (which is quite likely…) you have to write an email to the system administrator. By clicking on the z5 link under Resources a list of the administrators in your group is visible.
For more details about disk space consult the following IT-FAQ entries:
older stuff: