Issue: you would like to upgrade an existing Exchange 2013 server to SP1.
Background: The upgrade to SP1 is as significant of an installation process as the first time you installed Exchange 2013. Exchange 2013 is essentially installed again during the process.
Caveats: If this is a new deployment of Exchange 2013, then first install the Exchange 2013 prerequisites.
Required AD Schema Upgrade:
Exchange 2013 SP1 requires an AD schema upgrade, follow this link to prepare AD and prepare the AD Schema for Exchange 2013 SP1. Allow AD to replicate before proceeding with the upgrade to Exchange 2013 SP1.
Exchange 2013 SP1 Installation:
1) Copy the Exchange 2013 SP1 media download to the hard drive of your Exchange server(s)
2) Right click the setup.exe and click ‘run-as-administrator’
3) Proceed through the upgrade process and reboot the server at the end
Note: I recommend upgrading servers one at a time.
If you are upgrading an Exchange 2013 DAG to SP1 you can follow these steps for installing Exchange Service Packs and Rollups on DAG Members.