The AC in my 2003 VW Convertible is not chilling enough. What can I do about it?

Your system may just be low on freon. Most auto parts stores sell 134a freon for about $10 a can. If you visit an Autozone store the parts counter personnel might also show you how to add freon to the VW Beetle, it's not hard once you know where the correct port is located. You simply start your car, connect the freon dispensing hose to the AC port (there are two (2) ports, but the hose connection will only fit onto the smaller of the two (2) ports - the low pressure side). Allow the car to run while the can is discharged into the AC system, generally takes 10-15 minutes. Most dispeners have a freon pressure gauge on the hose portion that attaches to the can. Never disconnect a partially empty can unless there is a shutoff valve, and the valve is closed all the way. Better to add the entire can to the AC system.
If you have never added freon to your 2003 VW Beetle, that's the most likely problem. You could also have developed a slow leak in the compressor or AC lines, so I recommend adding freon WITH a sealant in the same can just in case.

The job would cost between $45 and $65 if you take it to a reputible mechanic to perform. That usually includes a full blown pressure test of the AC system. and a whole list of costly recommendations.