SP Upgrade is able to migrate (convert and transfer) the core data from Joomla! 1.5 (from now on called source) to Joomla! 1.6, 1.7, 2.5 or 3.x (from now on called destination) and above. You install SP Upgrade on the destination site, and you transfer items from the source database.
Installing the package is the same as with any other Joomla! component. Go to your site's back-end Extensions, Manage and click on Browse. Locate the ZIP package and click on Upload and Install.