The period of leave should not normally exceed 2 semesters and will not be accounted within your standard period of study.
The leave of absence has to be requested at the Studienbüro (study office). It will exempt you from the obligation to regularly attend lectures. No enrollment fee will be charged.
You can download the application on the website of the Studienbüro.
We dissuade from the option of de-registration, because it may endanger your place at the university and since you will lose your health insurance coverage.