I finally got my Magento 2.04 upgraded to 2.07 - after experiencing several frustrating issues. I'm not a technical person, so thought I would share my experience in hopes that it might help others who are also not technical:
1. Readiness Check - I experienced problems here with my cron jobs. Took me quite a while to figure out how to get those set up, but I was finally successful. Using an SSH terminal, logged in as root - I created the cron jobs. There was no information on how to actually create these (ie use the editor in the SSH terminal). A good source I found was: http://php-opensource-help.blogspot.com/2010/03/how-to-set-up-cron-job-file-using-putty.html.
2. Backup - This required several directories to have permissions updated. Got through that using CHOWN command. Then the backup failed. No message other than "server error". Turned out I needed to change the PHP max_execution_time to 1800 in order for the backup script to run successfully.
3. System Upgrade - my system kept hanging after ./composer.json had been updated. No error given on the log, it just sat there. Eventually I found an error that was emailed to me (I'm guessing because of the cron jobs - but not sure). It turned out that I needed to edit my PHP.ini file and change the memory_limit to 10G. That fixed it.
4. Since my upgrade was hung on system upgrade - in order to get to the point that I could re-run, I had to go in and:
a. disable maintenance mode: php bin/magento maintenance:disable
b. deleted the var/cache directory content (this may have been unecessary, but it didn't hurt anything).
c. deleted from the var folder - update_in_progress.flag file
5. After the upgrade completed, then I had a ton of PHP errors again. It turned out that upgrading changed permissions and the ownership of several files and folders back to root. I ran in SSH: chown -R user/group <magento directory>. This changed all directories and files under my magento directory to the correct user and group.
SUCCESS! It only took me 8 hours to get through all this. But I am now running version 2.07 and have documented all so that hopefully the next upgrade will go much more smoothly.
