How to upgrade APS6 in cisco wlc 9800 ?

[palani2010]

How to upgrade APS6 in cisco wlc 9800 ?

Gui and Cli

[Mark Elsen]

  - Ref : https://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/technotes/8-8/Cisco_Catalyst_9800_Series_Wireless_Controllers_Patching.pdf
      Start reading from : AP patching using an AP service pack

   M.

[Leo Laohoo]

Applying APSP can either be done using GUI or CLI.  

In GUI, the upgrade is staggered depending on the iteration -- All the AP will download the new patch firmware and select APs will reboot until all APs have upgraded to the new patch firmware.

[Rich R]

I presume you mean how to install APSP6? 
You don't mention the WLC model or software version (which always helps) but the approach is generally similar apart from different images for different platforms.

Take a look at the recent discussion at https://community.cisco.com/t5/wireless/can-we-do-ap-predownload-in-advance-while-installing-apsp/m-p/5245237#M279629 where we discussed APSP install in great detail just last week.

The most important point to take note of is that there is a major bug in the GUI for APSP install - it does not allow you to pre-download to the APs.
So you either do it all on CLI or you do most of it on GUI but have to initiate the pre-download from CLI before proceeding with the following steps on the GUI as explained by @eglinsky2012 

If you do not plan to pre-download to the APs then you can use GUI with APs rebooting immediately when they complete the download (according to the staggered option selected).