I'm in the process of upgrading from 3.8 to 4.x. When I hit Step 7) Attachment System Alterations (4/5) it stalls out. I've read that it's because of my large amount of attachments - 31,000+.
I've also read that the update may not be the best idea right now and should probably wait until 4.1 comes along. Unfortunately I didn't read this until AFTER I started the update.
So the question is, how do I revert back to 3.8 with my php-admin backup?