Upgrade from ESX 3.X - 3.5

I guess I'm just a little confused on the upgrade process so any advice is much appreciate.

I understand I can get the media, stick the CD in and upgrade the server.  What is vmware update manager? Can I use it to update my esx host?

Also, for the VirtualCenter 2.5 server, where is that installed from, same CD?  Is there an upgrade document somewhere detailing the order the upgrade should be done in?

Is there an update to the vmware license server as well?  Do you need new license files?

Any help is much appreciated.

Thanks,

Shawn