(Note: The purpose of this post is not to teach about five hole octaves. It’s simply a tip for those already starting to use them in their playing.)
Learning to switch between four five hole octaves can be a pain. Something I found useful is learning major scale folk melodies in the upper register and playing them using octaves exclusively. Not only do they sound great by themselves but they really give you a workout in swapping your embouchure between the four hole blow and five hole draw octaves.
An added benefit is that it helps you intuitively learn the layout of the upper octave on your harmonica.
Let me know how you get on.