I tried modifying config.php file but OpenX failed to run properly i.e. not without bugs. After several trial and errors, this is how I did it:

Image via CrunchBase

• Upload a fresh copy of OpenX script to the new web server.
• Create mySQL database and run OpenX install as usual until finish.
• Drop all tables from the DB using phpMyAdmin check all and drop.
• Then you need to restore your original DB from the old server. As my MySQL database grew quite a bit (32MB) in size, usual cPanels’ database ‘restore’ or phpMyAdmin ‘import’ failed to work too. The trick was to split up the DB and you do this using phpMyAdmin ‘export’ function.

In my case, I wanted to break up the DB into two portions and as I noticed the biggest table was ox_data_summary_zone_impression_history, the first half of the split stops just before that table. Next split continues from it until the end.

I thought of deleting the history data altogether to reduce the DB size and makes importing easier but didn’t try out the idea. This is at the expense of losing your ads traffic data.

• I then ‘import’ the DB to the new web host one after another. This makes the transfer less technical as phpMyAdmin has restrictions on file size and upload time. If it timed out, you can just run ‘import’ again and it will continue where it stopped.
• Access your OpenX site as usual.

I hope this helps and work for you too!