Log in to your Managed Hosting Server via SSH
Add these two lines to .bashrc:
alias php5cli='/usr/local/bin/php5-56LATEST-CLI'
alias composer='php5cli ~/composer.phar'
Reload .bashrc with
$ source .bashrc
Install Composer with
$ curl -sS https://getcomposer.org/installer | php5cli
Done.
Check the installation with
$ composer -V
You should see something like this
Composer version 1.2.2 2016-11-03 17:43:15
Your version will probably differ.