How Do I Decrease Image File Size, Keeping Image Quality?

I have a 468×60 promotional banner and it is currently 69.3 KB and I need it to go down to 50 KB or under. Can anyone please let me know how to do this without losing any of the image quality or anything else. I want it to be Exactly the same, but just smaller in file size. Can anyone help? Thanks!

See original post by Sean101