I installed PHP 5.3 and 5.4 via Plesk and I can select one or the other version in Plesk, but the phpinfo() still shows old one even after reboot (5.3). I can turn new one with PHPManager in IIS itself (register new PHP as there is only one listed, 5.3 at the beginning), but that kind of beats the purpose of Plesk then? There must be a bug in here somewhere...