How to Make Lower Class Gain More Money
Peasants will always be poor, you need them off their subsitence farms to have any chance.
Other than that, Low taxes, cheap goods. If you oversupply so that the basic goods needed by the lower classes are so cheap, they can actually afford them, and have more money for other things.
There is also increasing minimum wages, which I generally found bankrupted anything other than very profitable factories, but that would also probably help.