Update a SESSION_VAR on form submit

hello, I have a Session variable $Stage which I want to update (increment by 1)when my form submit button is pressed. <FORM Method=\"post\" Action=\"$PHP_SELF\"> how can I update this session variable ? I dont want to update it at the start of the script, because if the Reload button is pressed, it will keep updating it and it will mess up the script Please can someone help me out. Thanks Pete