Go to Administration Panel. Click on templates. Select header on the drop-down menu. When it loads, search for:

<meta http-equiv=”Content-Type” content=”text/html; charset=$charset” /><title>$bbname - $versionlong</title>$css

Supposing you’re using version 1.9.6 SP1, to remove the SP1 substitute the code above with the following: <meta http-equiv=”Content-Type” content=”text/html; charset=$charset” /><title>$bbname - $versionshort</title>$css

To completely remove the version and powered by XMB. Substitute with: <meta http-equiv=”Content-Type” content=”text/html; charset=$charset” /><title>$bbname</title>$css