Either would work. Some folks prefer to switch to a slightly lower level of protein to "slow down" muscle development, allowing skeletal growth to keep up. Others, stay on a high 20% protein right through point of lay. I've seen all the data and I still don't know for certain which way is best. Flip a quarter I guess.
At only four weeks old I'd keep them on starter until they are at least eight to ten weeks. You can change over then if you want. Personally I keep them on starter until I get the first eggs. One less type of feed to buy and store.
Starter crumbles up to 8 weeks.
Starter/Grower, (until I get my first egg).
or
Grower Crumbles or pellets from 8 weeks until you get your first egg.
Layer from first egg on.
Now I put my chicks on 22% protein poultry pellets when they are around 12 weeks old. If I have any starter/grower left, I mix it with the layer until it's gone. I haven't had any problems with my girls laying.
I have been mixing in a little grit with the starter grower since my chicks were about 3 weeks olds. They are now about 6 weeks old. I don't know if I am giving them the right amount. How much is the right amount for 10 chickens at this age? I have a mixture of Rocks and Black Australorps.