Well, if you don't even know what you're trying to do, it's going to be very hard to help you do it!! ;-)

Think about the voltage divider: it's all to do with ratios, isn't it?

Draw the diagram; think how the "output" voltage from the divider (that you measure with your ADC) is related to the "input" voltage to the divider.

You also need to think about how the range of ADC digital output values relates to the range of analogue input voltage values to the ADC.

Putting these together, you should see how the range of ADC digital output values relates to the range of analogue voltage values on the "input" to the divider.