EX2010 SP2 Schema update

Hi

We have an existing mixed EX2003 & EX2010(SP1) environment and will be upgrading to 2010 SP2 and need to clarify exactly what steps to perform for the schema update.

I've seen the link:

http://technet.microsoft.com/en-us/library/bb125224.aspx

But I believe some of these steps are only required for a new install but please correct me if I'm wrong.

We have two main domains (with tree root trusts) and the schema master (and the Exchange security groups)  is in a different domain from the actual Exchange servers. 

I've seen other links which state we only need to run "setup.com /ps"  while connected to the schema master.

Can someone help please ?

Thanks