Updating Drush to newer version on Drupalpro VM Virtual Machine Instance
Using a fresh setup of Drupal Pro VM image, all you have to do is just goto the drush directory and do a git pull from there to pull in the latest code from drush's repo. This is what i did:

cd ~/drush

git pull

git checkout 7.x-5.9

You can load up another drush version by just listing out the ones available by doing a git tag