You can connect up a external antennas to help increase ranges. There are various antennas that you can connect. The 4500 has 3 so it might depend on what band you use mostly and which antenna to use.
I would also see what band and mode you really need. If you don't need the Mixed Mode of WiFi, try using a dual or single mode to get better range of signal. Some people use G mode only at 2.4Ghz and have better range. If you don't have any devices that use A/B then switch to dual or single mode if there isn't a real need for mixed modes. Mixed modes shortens the range.