How to manage Airport Extreme from Windows PC?
I have not had a PC for a few years, but if I did I would use AirPort Utility 5.5.3 for Windows to administer the AirPort Extreme.
How to connect at 300 Mbps?
The following may help to connect at the fastest available speed:
Make sure that the PC is capable of connecting to a 5 GHz network. If you are not sure, you may need to contact the PC manufacturer or post the question on a PC forum.
Keep the PC close to the AirPort Extreme....same room, line-of-sight between the PC and AirPort Exteme.
Recommend that you use WPA2 Personal security settings.