To see all your environment variable open a konsole and type
you can pipe the results through grep to narrow it down
env |grep kde
To change them you have to export them in the .bashrc file. This file is in your home directory.
For example, this line will set the $JAVA_HOME variable to this path
But it depends what you are trying to do. KDE sets its own variables so it knows where to find its own files, changing them will affect the way your desktop behaves.