Simple, Audacity. You can use the following tools to improve the quality of your audio:
- Most cheap Microphones cut the base. Boost it back to normal with the Equalizer.
- Add a few seconds of silence to your audio and you can eliminate background noises with Noise Reduction.
- No matter how great your Mic is, the change of the volume of your voice can be annoyingly huge. Change it with the Compressor.
- If you scream a lot, or the changes to the audio made it too loud, you can fix all the overmodulations with Normalization.
All of these effects work very well, allthough you may need to play around with their preferences