Change order status function

Hi, I am looking for a woocommerce function that will let me change an orders status to completed.

I found a filter/hook – woocommerce_payment_complete_order_status but that isnt exactly what I need, I want to be able to run something like:

change_status($order_id);

and have that order id changed to completed.

Thanks for any help.

http://wordpress.org/plugins/woocommerce/