Right, this is a fairly easy procedure. However, when I first touched an IOS-XE bin image I managed to nicely transform a stack of 3 x Catalyst 3850 into a lovely expensive brick. This happened back in 2014 only because I thought I have to change the boot statement to “tell” the stack what file to use to boot. I was very wrong and that caused me a lot of pain and misery. I also hit a bug with that particular version of code. About bugs, in a different post.
Just double check the running version of code, make sure you’re on 3.x.x and follow the below steps:
