1. Download the 3.4.2 source files from here


2. Extract it to a temporary directory within your Downloads folder


3. Open a terminal session.


4. Navigate to the folder with cd ~/Downloads/Python-3.4.2



5. As per the Python documentation, run the following commands from the terminal:

   
   
   

   ./configure
   
   make
   
   make test
   
   sudo make install
   
   

This will upgrade your existing Python-3.4 installation to Python-3.4.2 (accessible as python3)