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).