Nice tutorial! I use A, A7, D, D7 or C, C7, F, F7 progression and whisle melody. I like version with 7s between chords a bit more, its has a little twist which i really enjoy!
So are we not gonna talk about how the strumming pattern is the same pattern as somewhere over the rainbow by Israel Kamakawiwo'ole? No just me? Alright.
focus on playing one chord for a few minutes then try and switch to the next chord slowly. making sure your finger placements are in the right spots. try slowly switching between those two chords for 10-15 minutes and then switch between them faster and then faster. That helped me when I was learning :)