This is pretty simple, but for some reason hard to google4.
1) download the latest Kickstart and System image from cisco.com
2) tftp, or whatever method you like get the image onto the Cisco
3) Run this on cisco console in “config” mode
a) boot kickstart bootflash:/m9100-s2ek9-kickstart-mz.5.0.1a.bin
b) boot system bootflash:/m9100-s2ek9-mz.5.0.1a.bin
4) Save your Config, Reboot the Switch..and your done.
You probably don’t want to skip versions, i.e. 3-5 directly.
You can probabaly only hold 2 versions at a time, so if your on 3, upload 4, upgrade to 4, delete 3, then upload 5, update to 5, rinse, wash, repeat.