What's the speed you're paying for with your cable co?
You can check the speed at a number of sites, on of which is
https://www.speakeasy.net/speedtest/
You can also test if it's a wireless issue by plugging your computer directly into your AirPort with an ethernet cable to see if it improves the speed (which would confirm that it's a Wifi issue)
Also open AirPort utility and see if you need to update the firmware (it will tell you if it does)