Custom Code for Infopath Form Button click Event

hi

i have one concern that i want to write the custom code for the button for saving the existing infopath form in to the Sharepoint Form Library, because if i use the submit button it is adding one more new form instead of updating the existing form.

for the first time the submit button is ok , but if i want to edit the infopath form it is saving a new form.

is there any way that it will update the existing form and close.

sal