I use Audacity for all of my conversions. You can download
Audacity here:
http://www.audacityteam.org/download/windows/Then scroll down and download LAME MP3 encoder from the same page.
If you look at Audacity you will see that you can do a lot more than conversions with it.
When converting a wav to a MP3 you can choose from many data compressions. Click on File/Export Audio and scroll down to MP3 files in Save as type. Then click on Options and pick your kbps in the scroll down arrow in the Quality window: see attached image.
