The extension of a Schengen visa will only be considered if you need an extension because of serious occupational/personal reasons, humanitarian grounds or force majeure. You will otherwise be required to leave the country for a minimum of 6 months and reapply for a new Schengen visa.
It is possible to extend a Residence Permit. To do so you need to go to the aliens registration office (Ausländerbehörde) located in Wedding at Friedrich-Krause-Ufer 24 no less than 6 weeks before your visa is due to expire.
You will need to bring with you:
- A visa application form
- Your residency permit
- Your passport
- Two photographs (passport style)
- Proof of income
- Documents to support your stay – letter from your employee, letter from your university, proof of financial independence for non-working applicants.
This office is only open on Mondays, Tuesdays and Thursdays, and it is strongly advisable to get an appointment.
http://www.berlin.de/labo/auslaender/dienstleistungen
The website also allows you to download the application for residency permits and the application, which is in four different languages, including English.
Your application will usually take between 1 – 2 weeks and will cost you €60 for 1 year (€30 for minors).