title: how do I remove other python versions and keep on just python 3.5
body: <p>I have installed Python3.5.6 but when I check my terminal I found that I have also Python 2.7.15rc1 and Python 3.6.7
  When I type Python, I leads to Python 2.7.15rc1
  When I type Python3, I leads to Python 3.5.6
  When I type Python3.5, I leads to Python 3.5.6
  When I type Python3.6, I leads to Python 3.6.7</p>
  
  <p>Please help because I can't install packages like numpy using pip3 on Python 3.5</p>
  
  <p>I want to keep on just Python 3.5</p>