Changing Python Versions in Ubuntu 16.04

[ErnestTBass]

I have three versions of Python on my laptop. They are Python 2.75, Python 3.5.2, and Python 3.6.2.

When I invoke the command

Python -V

I get the Python 2.75 version. That was fine in the past. Now I want to invoke Python -V and get the latest version Python 3.6.2.

Also, when I run jupyter notebook,it uses Python 2.75. I want it to use Python 3.6.2 instead.How do I change that?

I believe that these are really the same question.By changing Python -V to Python 3.6.2, I will have changed the default
Python interpreter to Python 3.6.2 in jupyter notebook.

Any help appreciated. Thanks in advance.

R,


ErnestTBass