Everything is perfectly explained in this post:
http://ubuntuhandbook.org/index.php/2013/08/install-gcc-4-8-via-ppa-in-ubuntu-12-04-13-04/
List of commands
sudo add-apt-repository ppa:ubuntu-toolchain-r/test sudo apt-get update; sudo apt-get install gcc-4.8 g++-4.8 sudo update-alternatives --remove-all gcc sudo update-alternatives --remove-all g++ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.8 20 sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.8 20 sudo update-alternatives --config gcc sudo update-alternatives --config g++ gcc --version
