Prepare your computer hardware for audio and video editing. Aside from a computer with the right video and audio editing software, you need to have quality speakers connected to the computer so that you can properly edit the sound elements in your video.
Choose the software you want to use to edit the video's sound. Many programs are available in the market for this purpose. The more popular choices include the freeware Audacity (for Mac and PC platforms), Adobe Audition (part of the professional production bundle of Adobe for both Mac and Windows platforms), Adobe Soundbooth (for amateur users in Mac and Windows platforms), Soundtrack Pro (part of the professional production bundle of Final Cut Studio in Mac platform) and GarageBand (for amateur users in Mac platform).
Although each program varies in terms of button and function names, menus and keys, all of them generally offer the same basic concept, steps and application when it comes to editing sound elements. All of them offer functions for cutting, extending, looping and enhancing the audio.
Open the audio files in your chosen sound-editing program. Make a new project so that you can save your work for this project accordingly.
Listen to the audio that needs editing and/or enhancement. At the same time, familiarize yourself with the densely packed vertical lines called waveform as seen in the program's monitoring window. Its longer parts show the louder portions of a sound file, while the shorter parts show its softer portions. You may write down the problems you encounter while listening to the sound elements. This can serve as your guide for the cleaning of the audio.
Even out the sound by determining which sections are unnecessarily louder or softer than others. The waveform works as a visual guide so you can better edit the sound volume. Most programs also feature "Auto Levels" or "Compressor" functions that can serve as more convenient ways of making the sound even.
Add audio filters and alter the equalizer to improve the sound quality, if needed. Names of filters and locations of these filters and the equalizer depend on the type of program used. Ideally, they are found in the menu or toolbar of the program. Popular audio filters include those that provide reverb or echo, alteration of pitch or duration of sound playback and change of the sound's background from a room to a forest or market.