jUpgrade is a Free Joomla 1.5 component would migrate all of the data from old Joomla 1.5 to the new Joomla 1.6 installation After that download a version of Joomla 1.6, decompress it and install it.

The steps to test it

1) Install the component in your Joomla 1.5 site.
2) Run the upgrade
More >