Hi DennisG,
Thanks for posting your question. I'm more than happy to assist you today. Joomla typically makes large changes from version to version. I'd advise you NOT to attempt to upgrade versions. However, we have a pretty extensive knowledge base of articles on Joomla 2.5:
Manually Installing Joomla 2.5Joomla 2.5 Tutorials
If you need further assistance please feel free to contact us.
Thanks!
Tim S