Open your PHP template and save it as sqlupdate.php.
You could read data from a table, delete that data and then replace it with different data. However, SQL lets you do it in one step.
Paste this inside the PHP block:
mysqli_query($dbconnection, "UPDATE first SET familyName='Addams' WHERE familyName='Adams' LIMIT 1;") or die("Error changing: ".mysqli_error($dbconnection));
Again the LIMIT is there for safety. The rest says:
update the row in the table which contains the familyName Adams and change that to Addams
Try that page and use sqlsort.php to check that it correctly changed the one record.
If you wanted to change more than one field you separate them with commas:
UPDATE first SET familyName='Addams', personalName='Jehoshaphat' WHERE familyName='Adams' LIMIT 1;