I decided to upgrade from 2.6.5-pl to the 2.8.4. I remember that I moved the standard manager location so as I understand I need to use advanced installation package. Do I get it correctly I need to unzip the package so that core merges with the current core directory (meaning newer files will be overwritten and new ones just added) and the setup directory would be placed in the site root?
You should be able to use the UpgradeMODX extra. It will handle the moved Manager or Core directories with no problem. Be sure to backup your site first. And make sure not to skip over any version ending in .0 as you do your upgrades.
Bob’s extra UpgradeMODX does a great job, and makes upgrading super easy. I use it on all my sites. And, as he said, make sure you upgrade to 2.7.0 first, then to 2.8.0, and then to 2.8.4
I should mention that with some older versions, you can run into a conflict between your PHP version and the version of MODX that’s running. In some cases, you’ll see PHP warnings and errors messages but the upgrade will still work. In other cases, you get a fatal error before the upgrade completes. The second one is pretty rare, but it’s still a good idea to back up the site.
I also run the ClearCache extra before and after every MODX upgrade I do. It’s very fast, and it eliminates a lot of problems.