ok when it comes to stack upgrade all switches in the stack needs to be on the same IOS or else stack will be broken.
there is a very easy way to upgrade the stack in one go. Make sure you use a ".tar" IOS this is the one with GUI feature in it. Once you have the IOS downloaded on you computer foloow the below given doc to perform an IOS upgrade as there is a diff way to upgrade with .tar file and TRUST ME its the easieast way to do that :-
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...