itunes 10.6.8 on Leopard doesn't allow me to use iTunes Match. Help!!!

Hey guys, so I'm running the latest version of iTunes available for 10.5.8 and I want to introduce iTunes Match into it. While iTunes supports it, it keeps saying that I have reached my limit of how many authorized machines I can have on my account. I took off machines and iDevices that I no longer use and it still says I am at my limit. I have a total of 4 Macs and iDevices combined on my account. Anyone have some helpful info on how to solve this? Thanks.