Update total shipping cost using ajax

hello every one,
i am working on woocommerce and i am stucked into a problem i want to manage shipping cost myself on cart page and checkout page so wrote some code i updated some code using wp_loaded hook and written myself code for get_zone_matching_package() function and it is working fine for when shipping cost calculted using php but when i changed country means using ajax it is not working properly i am unable to find the flow for ajax please some one help me out
thanks