You just want to call one or the other function when the checkbox is ticked or not.
<input type="checkbox" onChange="changeContent('vadiv');" value="'value'" id="vbook'" name="vbook"/>
//what need to be accomplished if box ticked
//what need to be accomplished if checkbox is unticked
I see no reason to use two functions changeContentA and changeContentB to change the content of the element "vadiv" into another checkbox.