need help with song for reverberation

I recently deleted a song off of reverbnation, edited the song a slight bit, and now the song is too long for the website to upload and i need to make the mp3 smaller.
Do you know how I can do this?

I make music with Garageband, i convert the file to mp3 and send it to iTunes. I just downloaded Audacity earlier and have been reading tutorials and etc but I still do not seem to understand.
my mac is a OS X 10.9.2
I am using Audacity 2.0.5

I am just trying to make the mp3 less than 8 MB so I can upload the song. Right now it is at 11 MB and I am not sure how to make the size smaller and then be able to upload it.
any help from the pros is appreciated. thanks

Instruction for changing the MP3 compression settings are here:

Note that re-encoding an MP3 will reduce the sound quality, so it is highly recommended that you make a new MP3 from the original Audacity project, or from an original high quality uncompressed file format such as WAV or AIFF.

The minimum recommended bit rate for reasonably quality stereo music is 128 kbps. Lower bit rates will produce smaller files, but also reduce the sound quality. For music, if you need to go lower than 128 kbps it will probably sound better if you first convert it to mono.

VBR encoding generally produces better sound quality than an equivalent size CBR encoded MP3, but some sites will only accept CBR encoding, so you should check the guidelines on the web site.

128 kbps CBR produces files that are very roughly 1 MB per minute of audio.