how do we turn our hot water down?

we have our heating on for three hour in the morning and from 4 til 10 in the eveing , the boiler is an old ideal mexico from the late seventies or eighties but seems to work fine , we have a similarly aged potterton timer. i have turned the orange dial down to 1 but doesnt seem to help unless it takes time for it to adapt ie 24hrs? do we have to do something with the copper storage tank instead if so it is new but doesnt have a thermostat on it altho there is an old style red tap which has vague numbers on it. any thoughts?