How to override the checkbox checked property

In the JavaScript page I have three checkboxes - 1, 2 and 3 of which the 1st box is always checked (I used checked="checked") on page load. If the user uncheck the 1st box, check 2nd and 3rd box and save. Now on page load the 2nd and 3rd box should only be checked. How can I achieve this? I am new to JavaScript. Thanks