After doing what Jet suggested to bring the Radio Stack up...
Click with the mouse in each section of the Radio Stack, a + or - will show, clicking with the + sign will increase the frequency, clicking with the - sign will decrease the Frequency.
This applies to all sections of the Radio Stack.
The Default Cessna 172 Trainer is a good aircraft to learn your skills on!
Paul....
...!
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.