PHP variable - assign a value Using JavaScript

Hi,
How do I reload a page so that I can set a PHP variable?

The code below triggers when a checkbox is checked, I then need to reload the page to set a PHP variable.

function pickup(pickup){
            if (pickup.checked == 1){
            document.getElementById('showmessage').style.display = 'none';
            document.getElementById('showbuttons').style.display = 'inline';
            //code to reload page here and POST or GET a variable that I can pickup and assign using PHP

            }else {
            document.getElementById('showmessage').style.display = 'inline';
            }

}

Thanks in advance for your feedback.