Just tried installing Exchange 2013 CU5 and is pretty much easier and went clean without any errors/warnings in my lab setup.
For the changes and fix that have been done in CU5 can be referred in my previous article
The setup can be downloaded from this location
As we are aware that the upgrade order from Exchange 2013 if we are using separate server for mailbox and cas then Microsoft recommends to upgrade the mailbox server first and then the cas server.
After the download is complete just open the setup file and it opens the below screen.Choose the required option its always recommended to check for updates and then click on next.
The setup starts copying files .
And then initializes the setup as below.
Finally it brings the upgrade option and just click on upgrade
Click on accept in the license agreement and proceed with the installation.
Now the setup goes through the prerequisites analysis
The setup starts once the prerequisites is completed.It goes through 18 steps as below for organization preparation.
Just reboot the servers after the installation is complete.
We can now notice the new service Microsoft Exchange Shared cache service is installed on the server.
For unattended installation/upgrade you can refer the below technet article.