This will be merged into the install file for later releases, but in the meantime here are the steps.
First, download the file
. Right now I have this on my download section on dinerminor.com.
Next, BACK-UP your PHPNuke 5.2 DB and files. This has had a very limited test.
Edit the information in the upgrade file to match your DB info.
Run the file.
Now, delete ALL PHPNuke files.
Finally, follow the instructions for upgrading PostNuke .5.3 from PHPNuke 5.1 in the README_FIRST file.
And that should do it.