How to diagnose and fix a faulty air conditioning in an Audi A2?

I've noticed that the air conditioning in my Audi A2 is no longer blowing cold air. What could be the possible causes and how can I troubleshoot and fix the problem?

Start by checking the refrigerant levels in your Audi A2's air conditioning system. Low levels could indicate a leak and will require a professional repair. However, if the levels are fine, you may need to replace the air conditioning compressor.