Uncheck a Radio button in Javascript using the class

Here are my 2 radios buttons :

 <input type="radio" name="sex" id="Button1" class="Button"/>

 <input type="radio" name="sex" id="Button2" class="Button"/>

When I call a function that countains :

document.getElementById('Button2').checked = false; 

It unchecks the Button2. But I want to uncheck it by using the class

And when the function contains :

document.getElementsByClassName('Button').checked = false;

It does not uncheck the Button2

Why and what is the solution ?

Thank you. :)