I have this PHP page where the user can select and un-select items. The interface looks like this:

Now I'm using these code, when the user hit the save changes button:

foreach( $value as $al_id ){ //al_id is actually location id
    //check if a record exists
    //if location were assigned and leave it as is
    $assigned_count = $this->AssignedLoc->checkIfAssigned( $tab_user_id, $al_id ); 

    if( $assigned_count == 0 ){
        //else if not, insert this new record
        $this->insertAssigned( $tab_user_id, $company_id, $al_id );
    }

}

Now my question is, how do I delete the un assigned locations? For example in the screenshot above, there are 4 assigned locations, if I'm gonna remove (or unassign) "Mercury Morong" and "GP Hagonoy" from the assigned locations, only two must remain. What are the possible solutions using PHP?

Thanks for any help!