{exp:channel:entries channel="news" entry_id="18" dynamic="off"}
	<?php
		$searchArray = array("old");
		$replaceArray = array("new");

		$intoString = "{title}";

		echo str_replace($searchArray, $replaceArray, $intoString);
		// Results in "old title" changed to "new title"
	?>
{/exp:channel:entries}