Thanks for clarifying on that.
Unfortunately, Apple dropped this "feature" along with a number of other things in the AirPort Utility 6.x versions.
If you have any Macs there still running Snow Leopard, you can download AirPort Utility 5.6.1 and find the feature that you need.
Or, if all of your Macs are running Lion, and you are willing to bypass the warning that AirPort Utility 5.6 for Lion may not configure the device correctly, you can give that a try. It does seem to work for me, but your results may vary.