How do I trim highs and lows?

I'm hoping someone can kindly advise me. I'm nearing the completion of a project (17 tracks) and I have mixed and exported them as uncompressed wav files.

I'm using NCH Wavepad as an editor and I would like to have a neat trim on the peaks and lows (like as if cut across with a craft knife or scissors) as most 'good' audio files look.

Can anyone advise me on how to do this? 

Thanks! 

Sonar 8.5 Producer
Izotope Ozone 5
NCH Wavepad