I strongly recommend you keep an archive copy of every Exchange Server installer, service pack, update rollup, and cumulative update in case of a support or recovery scenario that requires it.
FAQ: In What Order Should You Install Service Packs, Update Rollups, and Cumulative Updates?
Which order should you install Exchange Server cumulative updates, service packs, and cumulative updates in?
How to Build an Exchange Server Test Environment
How to build an Exchange Server test environment and use it to test new updates.
Exchange Server 2013 Transport Services Won't Start After Service Pack 1 Upgrade
Exchange Server 2013 Transport services not starting after the upgrade to Service Pack 1 due to issue impacting third party transport agents.
Upgrading Exchange Server 2013 Servers to Service Pack 1
How to upgrade an existing Exchange Server 2013 deployment to Service Pack 1.
Exchange Server 2013 FAQ: Where is Cumulative Update 4?
What happened to Cumulative Update 4 for Exchange Server 2013?
Exchange Server 2013 Service Pack 1 Released
Microsoft has announced the release of Exchange Server 2013 Service Pack 1, containing several new features, improvements, and bug fixes.
Exchange Server 2013 Service Pack 1 Announced
Microsoft has announced that they plan to release Service Pack 1 for Exchange Server 2013 in early 2014.
Installing Cumulative Updates and Service Packs for Exchange Server 2013
The step by step guide for installing Cumulative Updates and Service Packs in an Exchange Server 2013 environment.
Installing Exchange Server 2010 Service Pack 3
How to install Exchange Server 2010 Service Pack 3 to an existing Exchange Server environment.