I assume you mean channel instead of frequency.
First see which wireless channel is being used by checking DeviceInfo under Status. Then go to Manual Wireless Network Settings under Setup and turn off Enable Auto Channel Scan.
Then set the Wireless channel to a different channel. Try 1, 6 or 11 unless it was previously set.
You can also download inSSIDer from http://www.metageek.net/ and see which wireless channels are being used near you. Then pick the channel that has the fewest strong signals.