Hi Marlon,
You change the frequency on the AP via the Channel settings. This is an excellent idea to try and use different non-overlapping channels than your neighbour AP's. You probably want to tune the Transmit power as well. As always, a Site Survey is highly recommended :)
Each 2.4-GHz channel covers 22 MHz. The bandwidth for channels 1, 6, and 11 does not overlap, so you can set up multiple access points in the same vicinity without causing interference. Both 802.11b and 802.11g 2.4-GHz radios use the same channels and frequencies.Cisco recommends that you assign a static channel setting for each AP.
This doc shows the IOS commands;
http://www.cisco.com/en/US/docs/wireless/access_point/12.2_15_JA/configuration/guide/s15rf.html#wp1037361
Hope this helps!
Rob