I just upgraded this morning from 4.85.
This is what I did:
1. Back up your database and all your PhotoPost files in your /gallery directory.
2. Unzip version 5.11 on your computer.
3. Compare your new (local) config-inc.php and config-int.php file with ones on your server, and make needed changes to local ones.
4. Upload all the files and directories to your server - install.php file not needed, but if you do upload it, make sure you delete it after upgrade.
5. Change permissions as follows:
images (chmod 755)
uploads (chmod 777)
help (chmod 755)
data (chmod 777) and all the subfolders within like:
1 (chmod 777 - including subdirectories)
2 (chmod 777 - including subdirectories)
500 (chmod 777 - including subdirectories)
languages (chmod 755) (all subdirectories, too)
english (chmod 755)
6. In your browser, go to: http://www.yoursite.com/photopost/upgrade.php
From there, select 4.85/4.86, and all the steps will be completed for you, no need to upgrade version by version.
note: in this step, i had several pages listing error messages, along the lines of 'permission denied in .......xxxxxxx.php etc. I just scrolled down to the bottom and click on next or proceed buttons. It installed witn no problems.
7. Delete upgrade.php (install.php) file from your server.
Works like charm.