if it's on a nearly stock stang with a few bolt on's then you really dont need a larger MAF cause you wont gain performance if anything you can loose HP, but if its S/C'd then you could get a bigger one and have it calibrated to your injector sizes and all that neat stuff....
The MAF is a sensor that measures the amount of oxygen entering the intake. The computer uses this information to send the correct amount of fuel to maintain the air/fuel mixture. If you significantly increase the amount of air entering your engine, such as with a supercharger, you will need a larger MAF to handle the increased airflow. Otherwise, just keep the MAF you have.
your maf sensor translates the airflow into a certain number of volts which it turns into a number. the max a stock maf can read is like 4 volts or 5 volts, and the highest number it can read is around 1200. My car has the paxton on it and at 4800rpm my maf is around 990 which means it is very close to pegging out. i couldnt run my car any higher because it was dangerously lean, but you can see that it was well on its way to pegging. So really if you are less modified than me, you dont need a new one.