At first I installed Ruby using the default apt-get command, then I realised it is an older version. Ubuntu doesn’t keep maintain a latest version on their repository. So to remove the original one.
You can check where the current Ruby installed location by
$ruby -e 'puts $:'
To remove all the ruby installed
$sudo apt-get purge ruby rubygems
Then use RVM to install Ruby
$sudo apt-get install ruby-rvm $rvm install ruby-1.9.3-p125</p>
The installation process might take a while depends on the machine power.
To select which version of ruby to use, in case you have a lot different version of ruby installed on rvm earlier.
$rvm use 1.9.3-P125 $rvm list $ruby -v