It is very easy to check/uncheck a checkbox using jQuery. To do so you need to use the attribute checked and alter that. With jQuery you can do in this way:
12 $('#myCheckbox').attr('checked', true); // Checks it$('#myCheckbox').attr('checked', false); // Unchecks it
However, some cases you can not trust .attr() method to get the value of the checkbox (if you need to). You will have to rely in the .prob() method.
So, for jQuery 1.6+
You can use the new function .prop() as:
12 $('#myCheckbox').prop('checked', true); // Checks it$('#myCheckbox').prop('checked', false); // Unchecks it