I know this might seem obvious, but it seems to be frequently misunderstood.
When you get a PHP warning that says "____ is deprecated. Use ____ instead", it doesn't mean that you should just change the name of the function.
It means that you should go to the PHP manual ( [php.net...] ), look up the function you were using, look up the new function, and change your code so it uses the new function properly, using the rules and requirements for its use.
The two functions are often very similar, but they won't be exactly the same.