EF can be improved with exercise, but I want to point out that depending on the technician who did your echo or the machine it's very easy for the difference between the two readings to be caused by machine/technician error. I've had my LV wall measured at both 7mm and 13mm, pretty big difference when dealing with the heart.
It depends on the cause and exercise could cause more harm than good depending on that cause. I would speak with your Doctor about this and see what he/she recommends.