How to Change the BitRate in iTunes ?

iTunes>Preferences>General, then Import Settings and under the Setting drop-down menu I suppose you could just change the bitrate to something smaller than you currently have. You should know though that doing this will greatly reduce the quality of the song. Then convert it to whatever file-type you have chosen at your new, smaller bitrate. I wouldn't really recommend this because it will probably make the song sound like crap. How big is the file and why do you need it smaller?

I see. Well like I said, once you change the importing settings, control-click (or right click) on the file and then choose "Create MP3 Version" or whatever codec you have chosen. It should then convert it to a much smaller size. That probably wasn't very clear in my first post.