Dear shopgirl,
Why don't you download the latest Joomla 1.5.4 from joomla.org and install it yourself? Detailed instructions for downloading and installing joomla is available in that site. If you are hosting your site with hostmonster.com, another option is also available. You can install the latest Joomla1.5.4 version using the 'Simplescripts' option in your control pannel. I am using the hostmonster account and that is how I came to know this. If you want to do it manually, I can help you. please let me know.