A.H.
My boys are only 25 months apart, but our jealousy issue was very minimal. My best advice is: change the baby on the bed or floor, where your 4 year old can see everything. Have him bring you the diaper/wipes and explain everything as you do it. Also, when your 4 year old asks for your attention, like playing a game or reading a book and you are busy with the baby, tell him that you'll read the book or play the game as soon as you're done changing the diaper or feeding the baby and then do it, even if you don't have any help at the time and that means that baby is going to cry for your attention for 5-10 minutes. The 4 year old needs to know that you'll make him top priority at times, just like the baby. Lastly, when my older one came to see us in the hospital, we had a gift wrapped up for him that was from his baby brother because he was going to be the best big brother ever. He still knows (and will always know) that gift was the first gift his little brother gave to him. He'll even tell me, "Ryan gave this to me because I'm the best big brother." Good luck!