The video below is a great guide to upgrade a Cisco WLC through the command line interface. There are two main reasons I recommend using the CLI versus the GUI:
- You get more status updates for each step as it completes in the command line versus the GUI
- You can upload the software ahead of time, before your maintenance window. The software is not applied until you reboot so you can upload and then wait to initialize the reboot until you are ready
Pretty straight forward otherwise. This video shows the process very well!