The easiest method is right around the 1 1/2 year mark, get 5 new pullet chicks. By the time they're ready to start laying, the current ones will be 2, and you can give them away or sell for $5 each, or make soup or whatever. Or buy older birds that are already 4-6 months old.
I've heard of "pimping out" chickens, but bio security is a worry of many. Plus with hatching eggs, you'll have no guarantee to gender. You could get 10 boys and 2 girls, or 50/50, or some other mix. Then you'd have to figure out what to do with the boys.
I've been adding in groups of 2 to start my flock. In a continual phase of renewing it, I guess you could say. The original 4, 2 were 1 1/2year old, the other 2 4 months old. The next 2 were 8 months old. The newest 3 I hatched myself, and luckily only hatched one boy, and had an extra hen to go with him as a pair for an easier re-home. They're now 4 months old.
So I have two laying every other day, the older ones. Not spent yet! 2 laying every single day, giant brown eggs. From the "yearlings". The next youngest two just started laying, every other day, likely because of their breed. Not a production breed. The 3 new babies, when they start laying, the oldest 2 will be given away. In a year or so, I'll need two more to replace the next oldest two.
That way I'm not replacing the whole dang flock at once. Gives me a reason to buy eggs online once a year and keep a couple girls. LOL This time I opted for ducks, and if they go as planned, I'll reduce the chickens by 2, and sell the novelty breeds that don't lay that well. Chickens that lay well for food, and ducks for fun and bonus eggs. I can't have a rooster, but I can have a drake! That will fill my hatching itch, having my own breeding ducks.