Unfortunately the cheesy spy film/forensics show lied to you when it comes to the power of sound editing so it will never be brilliant quality.
Still the easiest way (and if done properly the best if done properly is to use the equailisation options. In audacity this would be effect (pulldown menu) -> equilization
Bass is usually the low frequency sounds (500Hz is about the cutoff but it will sound less than brilliant a bit before that) so dull those (a custom filter would probably be the best option).
You might have to repeat the process two or three times too.
Edit:
If you run audio through FFDshow there is an equalisation filter in that to give you a better preview.