Cumulative Updates are a complete package of the software itself, so when you using it to update your server, you are actually reinstalling Exchange Server 2013 with all the updates bundled into one package. You can use this CU1 for a new installation as well. Exchange Server 2013 now adheres to a scheduled delivery model. In this model, cumulative updates are released every three months. Cumulative Update package will be released as a full refresh of the Exchange product and will be installed as a build to build upgrade.
Follow the below steps to upgrade Exchange Server 2013 to Exchange Server 2013 CU1 Note : Make sure you take a complete backup for your exchange servers before applying updates.
Download Cumulative Update 1 for Exchange Server 2013 from : http://www.microsoft.com/en-us/download/details.aspx?id=38176
Summary
With Microsoft Exchange Server 2013, hotfixes and service packs are not delivered anymore. Instead of the priority-driven hotfix release and rollup update model used by previous versions of Microsoft Exchange, Exchange Server 2013 now adheres to a scheduled delivery model. In this model, cumulative updates are released every three months.