Cannot update GCC to latest version

I am trying to update GCC using:

sudo yum install gcc-c++

And I receive the output:

Package gcc-c++-4.8.5-39.el7.x86_64 already installed and latest version
Nothing to do

For some context, I need at least version 5.4.0 to run PyStan 2.19 which is needed for fbprophet. Issue related to fbprophet is outlined here: https://github.com/facebook/prophet/issues/1272