There two ways you can upgrade or downgrade your VM instances.
a. Stop – configure – start
b. Minimum downtime ( by swapping the disk )
a. This is a very easy method to do this. The main disadvantage of this is, it requires downtime. If you are okay with a 5 – 10 minute of downtime then you can go with this method.
b. If you this to happen almost real time then follow these steps