sudo apt-get remove gcc g++

Check gcc again:

gcc –version

Install gcc 4.9/g++ 4.9

sudo apt-get install gcc-4.9 g++-4.9

Checking Version:

g++-4.9 –version

Link to gcc g++

ln -s /usr/bin/g++-4.9 /usr/bin/g++
ln -s /usr/bin/gcc-4.9 /usr/bin/gcc

Checking Version:

g++ –v
gcc –v

Latest update:

mkdir ~/Downloads/gcc-4.9-deb && cd ~/Downloads/gcc-4.9-deb

wget http://launchpadlibrarian.net/247707088/libmpfr4_3.1.4-1_amd64.deb
wget http://launchpadlibrarian.net/253728424/libasan1_4.9.3-13ubuntu2_amd64.deb
wget http://launchpadlibrarian.net/253728426/libgcc-4.9-dev_4.9.3-13ubuntu2_amd64.deb
wget http://launchpadlibrarian.net/253728314/gcc-4.9-base_4.9.3-13ubuntu2_amd64.deb
wget http://launchpadlibrarian.net/253728399/cpp-4.9_4.9.3-13ubuntu2_amd64.deb
wget http://launchpadlibrarian.net/253728404/gcc-4.9_4.9.3-13ubuntu2_amd64.deb
wget http://launchpadlibrarian.net/253728432/libstdc++-4.9-dev_4.9.3-13ubuntu2_amd64.deb
wget http://launchpadlibrarian.net/253728401/g++-4.9_4.9.3-13ubuntu2_amd64.deb

sudo dpkg -i gcc-4.9-base_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i libmpfr4_3.1.4-1_amd64.deb
sudo dpkg -i libasan1_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i libgcc-4.9-dev_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i cpp-4.9_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i gcc-4.9_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i libstdc++-4.9-dev_4.9.3-13ubuntu2_amd64.deb
sudo dpkg -i g++-4.9_4.9.3-13ubuntu2_amd64.deb