where to insert hreflang?

Hi Guys!
as we know Google has made some changes. I would like to add hreflang to my web-site, but do not know how.
E.g.:
<link rel=”alternate” hreflang=”en-br” href=”http://www.example.com”&gt;
<link rel=”alternate” hreflang=”en-ie” href=”http://www.example.com”&gt;
<link rel=”alternate” hreflang=”en-gb” href=”http://www.example.com”&gt;

Where to insert that? Into header.php?