This question already has an answer here:
I was using Drush version 5.3 in my remote server with no problem at all. I got it working just uploading the the tar.gz from drupal.org to the root of my server. Then I could use commands like: drush/drush cc all, drush/drush cron,... So far so good.
Now I need to update Drush, then I downloaded drush from: https://github.com/drush-ops/drush and did the same: I uploaded the drush folder to the root of my server. But when I try to run a command like drush/drush cron I get this message:
Unable to load autoload.php. Drush now requires Composer in order to install its dependencies and autoload classes. Please see README.md
What does this mean?