Ironically AU 5.6 for lion will not install in Lion after about .2.. so 10.7.5 you are already out of luck.. Apple decided you no longer should have such a useful utility.. but it is easy to fix.
Here is one method.. just search there are many people who have listed it.
How to load 5.6 into later Lion & ML
1. Download 5.6 for Lion.
Click to open the dmg but do not attempt to install the pkg.. it won't work anyway.
Leave the package open on the desktop so you can see the file. AirportUtility56.pkg
2. Download and install unpkg.
Run unpkg on the desktop.. If your Mac refuses to run the software, because it wasn’t downloaded from the Apple store, go to security in preferences and allow other software to work.. this is limitation of trade methinks. You can set back later if you like.
Now drag the AirPortUtility56.pkg file over to unpkg.. and it will create a new directory of the same name on the desktop.. in finder, open the new directory, drill down.. applications, utilities .. there lo and behold is Airport utility 5.6 .. drag it to your main utilities directory or just run it from current location.
You cannot uninstall version 6 (now 6.3 if you updated) so don't try.. and you cannot or should not run them both at the same time.. although I have had no problems when doing so.