On the results page you should probably just add a hidden form element to the page to forward the ID.. add it right before the </form> tag on line 591 like:
<input type="hidden" name="ID" id="ResultsID" value="<?php echo($_GET['ID']); ?>" />
Then on the update page do the same thing, but set the value from the recordset like:
<input type="hidden" name="ID" id="ResultsID" value="<?php echo($row_WADApractice_contents['PracticeContentPageID']); ?>" />
Put that one on or near line 295 just before the </form> tag as well.