Usual mistake with people new to the sport is putting too much air in.
Going from 4 to 5 makes a big difference! Most experienced riders will notice quite easily.
And going down to 3 will make a hell of a difference when it's really slippy.
As for the front anything above 6 would be too much for me.
Quite often you see well meaning parents putting 4 in the rear for their child who weighs 6 stone when really 2 psi would be better. I know one child who runs less than 1psi.