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.

1. Download Cumulative Update 1 for Exchange Server 2013 from : http://www.microsoft.com/en-us/download/details.aspx?id=38176

   
   
   Double click on the file you downloaded, named Exchange-x64,  to extract setup files.
   
   
   
   
2. Choose/Browse a directory to extract setup files and then click OK
   
   
   
   
3. Once extraction is completed, open the directory where you have extracted setup files, then double click on setup.exe
   
   
   
   
4. On the Check for Updates page , select Connect to the internet and check for updates and click Next
   You can have setup download Exchange Server 2013 updates from the internet before you install Exchange. If no updates are found, click Next to continue
   
   If you don't have access to the internet or don't want to check for updates, you can select Don't check for updates right now and then click Next
   
   
   
   
   
   
   
   
5. Copying and preparing the necessary resources for setup will start
   
   
   
   
6. Setup will detect that you already have Exchange Server 2013 installed, and will inform you that you are about to upgrade your server. Click Next
   
   
   
   
7. On the License Agreement page, accept the terms and click Next
   
   
   
   
8. On the Readiness Checks page, setup will check if your organization and the computer you're running Exchange on are ready for Exchange 2013 CU1. It'll report any failures as errors. You'll need to fix any reported errors before you can install Exchange 2013 CUI, for example a pending reboot from a previous Windows Update needed to be fixed before proceeding.
   
   
   
   Once the prerequisites analysis reaches 100%, click install
   
   
   
   During the upgrade process, be informed that services will be stopped and then started again after installation is completed. So during this period, Exchange server will not be available to your users. If this is the only Exchange Server, then inform your users that exchange will be down.
   
   
   
   
   below you can find different setup steps:
   
   
   The last step is finalizing setup. Few seconds later setup will be completed.
   
   
   
   Once setup is completed, you can open Exchange Admin Center by selecting the checkbox Launch Exchange Administration Center after finishing Exchange setup and then click finish
   
   
   
   That's it, you have successfully upgraded Exchange Server 2013 to Exchange Server 2013 CU1

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.