Server SBS 2011 certificate problems!

Okay so we had a 3rd party company set up our server previously. I recently started helping doing IT here.

I like to think I'm pretty knowledgeable at a lot of things on windows...except certificates. I'm not exactly sure how to fix some of our problems.

We have a wireless radius server where the clients use to connect without having to worry with passwords using machine authentication. Problem is it stopped working today. After digging around I found out that some of the certificates expired. Problem is I have no idea how to renew them. They're just self signed ones.

How do I fix this?


ALSO

They must have set up the mail server to expire too. I ran the SBS fix it for me wizard, and it fixed it, but now it's getting me an error that the name is wrong. How do i change the certificate's name, because it's pointing at the wrong server.

PS

How do I simply decommission the mail server on our server? We are using our headquarters e-mail server now, I mean I'm getting certificate errors for a server we're not using anymore.