1 - ssh on the wlc;
2 - show sysinfo to check the running version of code;
3 - show boot - will show the code used to boot from and the backup;
4 - save running conf and download backup;
5 - download code on wlc;
transfer download datatype code
transfer download mode tftp
transfer download serverip 144.210.60.118
transfer download path .
transfer download filename AIR-CT5520-K9-8-5-135-0.aes
transfer download start
or much easier way via gui.
6 - predownload code on APs
config ap image predownload primary all
show ap image all to monitor progress
or
gui > wireless > global conf >
\\7 - show boot and/or config boot primary if necessary
8 - verify redundnancy is operational show redundancy summary
9 - reload > reset system in 01:00
or
reset system in 00:02:01 image primary swap reset-aps