Need to Search/Replace between link tags

I have an xml file that has various hyperlinks within <link>xxxx</link> tags.
I want to be able to replace all the various links with my own.
Is there a way I can search/replace every occurance of a <link> tag and replace with my own URL?
I dont need this coded, a simple manual process will do.

 

$xml = preg_replace('/<link>[^<]+<\/link>/', '<link>http://example.com</link>', $xml);

PHP:

 

I have a file called sample.xml,
how do I implement this code so it will give me a finished sample.xml?

Thanks