Q: how do I download higher bit rate songs from itunes match to replace the lower bit rate I have on my itunes library?

I have itunes match and I have about 500 songs that were ripped at 128kbps. I have been tolf that I can replace them via itunes match to improve them to 256 or 320?

I have put them into a playlist in my itunes library and I want to know how I can upgrade their bit rate via itunes match. Can anyone help me?