How to enroll for a Master? (Frankfurt)

Hi,

I already live in Germany, but would like to start a Masters in law (LLM) after I finish my post graduation in June. I currently study in london, but a master would be too expensive and I would like to have a degree from a German University.

Do you know how I can enroll for a course if I am a foreigner living in Germany? Are there special requirements (from government)?

What about the German "Zertifikat", do you know the most economic ways to achieve one?

I appreciate any assistance I can get. If you would like to contact me directly, just send me an email.

Best Regards,

Beatriz