Make a full copy of your site.
Copy all your files and the database so you can restore it if something goes wrong.
Find and download a new copy of your locale , for minimum PHPFusion 7.02.05
in the downloads sectionExtract these files and replace all your current locales in your /locale folder
Then download
latest PHPFusion 7 versionExtract your files
Find the upgrade file in v701/upgrade.php
Copy the file upgrade.php to your administration folder and replace current file.
Go to your administration > system admin select the upgrade icon, it should say that a new major upgrade is available.
Push the upgrade button and wait for your new config. When the config shows save the content that are shown in a text file on your desktop.
At this point your site will not work.
You need to copy all the files from your downloaded pack and replace the old files.
Once this is done, open your config and replace the content with the new generated content you have. Delete setup.php.
NOTE : If you still are missing some settings when upgrading from some really old versions, download the attached file add_settings.zip, extract, place it in root and run it.