If your Audio file is merely spoken word (as opposed to music) you can reduce the bit rate to 32kbps. One easy and free way to pull this off is through iTunes.

Here are the steps to make it happen:

1. Open iTunes preferences (file > preferences)
2. Choose the General Tab then the Import Settings Set Import Using to "mp3 Encoder"
3. Set Setting to "Custom"
4. Set Stereo Bit Rate to "32kbps" and click OK (twice)
5. Find the audio file in your iTunes music library.
6. Right click on it and choose "Created mp3 Version" - This will create a copy of your file with the smaller bit rate that you can then upload to your website.

Note: if your audio file is still larger than about 5 or 6MB, you may need to use FTP to upload your file to your site.