During some recent switch replacement work I did I noticed not all my stacks had the correct IOS version, or wai. The correct thing to say would be that one of the switches did not have the correct IOS version. The resone for this was that I upgraded to the correct IOS before I created the stack and then connected the second switch to the stack. When the second switch got connected the stack was left with 2 IOS versions.
To solve this issue I used the archive download-sw command to download only the new OS to the switch. To do this I first run show version to know the stack number of the switch.
From the show version I could get the stack number of the switch that needs the IOS upgrade. Be aware that the screenshot is showing the IOS version the same on all switches, so there is no difference in the screenshot. In my blog post I wanted to upgrade switch 2.
archive download-sw /destination-system 2 tftp://1.1.1.1/IOS.tar
To complete the upgrade and not to reboot the whole switch you enter the command
reboot slot 2
This will only reboot the switch that has the stack number specified.
Networks and rants 