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You can install drush to latest version or specified version.
I prefer drush 7, you can make this, first uninstall the current version of drush of your server.

i use debian, then i install with 

sudo apt-get install drush


and you need remove

sudo apt-get remove drush


and later install again with composer

curl -sS https://getcomposer.org/installer | php
sudo mv composer.phar /usr/local/bin/composer
sudo ln -s /usr/local/bin/composer /usr/bin/composer

sudo git clone https://github.com/drush-ops/drush.git /usr/local/src/drush
cd /usr/local/src/drush
sudo git checkout 7.0.0  #or whatever version you want.
sudo ln -s /usr/local/src/drush/drush /usr/bin/drush
sudo composer install
drush --version


and ready to use drush version 7