Mix about a teaspoon of any good dish soap in a half gallon of warm water. Place the mixture in a spray bottle and thoroughly soak undersides of leaves where the aphids are... Do this about twice a week for a couple of weeks to disrupt they breeding cycle...
If you can, collect lady-birds and place them on the plant or you can buy tagetes or french marigold plants, they don`t like the smell of them so soon fly off to your neighbour's garden.