HTML Code to create checkbox

<input type="checkbox" onclick="display(this)">Add more users</input>
<div id="yourDiv"> ...other forms... </div>

JavaScript function to hide the checkbox

 function display(e){
        if (e.checked)
        {
            document.getElementById('yourDiv').style.display = 'block';
        }
        else
        {
            document.getElementById('yourDiv').style.display = 'none';
        }
    }