The change from mysql to mysqli could be reasonably straightforward, depending on how the mysql is used in the code, e.g. classes/functions or vanilla embedding. PDO may be a little more work, but I'd go PDO as I find it cleaner.
Are you interested in doing this yourself if we're able to show you how? If yes, post snippets of code containing mysql usage. If not, as LM says, go to Business Exchange.