Students can be granted a leave of absence prior to or within one month of the official start of the semester if there is good reason. The application form is available here.
If you have already enrolled yourself for the coming semester you may hand in the refund application form in order to receive your semester fee back.
A leave of absence in the first semester is not possible. A leave of absence requires timely feedback and a re-registraion.
Further information as well as legal provisions on leave of absence can be obtained from the enrollment regulation para.8.