Raspberry-pi python shell still running older version of python

I am new to linux and somewhat new to python. I am trying to follow a tutorial that is using python 3.9, however I was using python 3.4.2. Once I realized I was out of date I downloaded python 3.9.0 and when I run

python -V

in the terminal is stats Python 3.9.0, but the python shell is still running 3.4.2

I am not sure how to change the python version for the current project, or start a new project in python 3.9 when I click on python 3 idle in the menu.

It still states python 3.4.2

So how do I get the python idle to run python 3.9.0 and not 3.4.2?

Answer

I have 2 python versions in my PC as well (2 and 3), what I usually do is to add an alias in ~/.bashrc, and update it when needed, example alias python="python3" or if python2 is needed just alias python="python2"