To turn register globals off, you will need to change the settings in the php.ini file to:
register_globals = Off
Note the upper case letter O in Off.
This will prevent PHP from automatically turning any value in the URL into a variable. That's a good thing because it means that hackers cannot try to insert anything they want into your code simply by inserting it into your URL. Well written code should be validating the variables anyway, but this provides extra security in case the script does not validate variables properly or if the validation is buggy.