Choose the version of ruby you want to install for example : 2.2.3

After choosing the right version of ruby first step is to install some dependencies :

sudo apt-get update
sudo apt-get install git-core curl zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev sqlite3 libxml2-dev libxslt1-dev libcurl4-openssl-dev python-software-properties libffi-dev

Next we can install ruby using any of the below three ways :

1) Using rbenv (Recommended)

cd
git clone git://github.com/sstephenson/rbenv.git .rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
exec $SHELL

git clone git://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
echo 'export PATH="$HOME/.rbenv/plugins/ruby-build/bin:$PATH"' >> ~/.bashrc
exec $SHELL

git clone https://github.com/sstephenson/rbenv-gem-rehash.git ~/.rbenv/plugins/rbenv-gem-rehash

rbenv install 2.2.3
rbenv global 2.2.3
ruby -v

2) Using rvm

sudo apt-get install libgdbm-dev libncurses5-dev automake libtool bison libffi-dev
curl -L https://get.rvm.io | bash -s stable
source ~/.rvm/scripts/rvm
rvm install 2.2.3
rvm use 2.2.3 --default
ruby -v

3) From source

cd
wget http://ftp.ruby-lang.org/pub/ruby/2.2/ruby-2.2.3.tar.gz
tar -xzvf ruby-2.2.3.tar.gz
cd ruby-2.2.3/
./configure
make
sudo make install
ruby -v