Installed Python 3 on Mac OS X but its still Python 2.7

Try typing python3 instead of just python.

While @rhombidodecahedron's answer is concise and to-the-point and @Nacho Izquierdo addresses your first question perfectly, my answer aims to answer your second question in some more detail:

One should not uninstall Python 2.7 which comes with Mac OS X; it is supplied by Apple and is needed for applications running on OS X. It is stored in /System/Library/Frameworks/... If it is removed, Mac OS X will have to be reinstalled.

Hope that helps! And to reiterate answers given by @rhombidodecahedron and @Nacho Izquierdo, install Python 3.x separately and use python3 if you would like to use that version.

Python 2.7 is the standard, Python 3.x is the future.