Installing python

[emaraiza98 at gmail.com]

I installed pycharm for a computer science class I'm taking, and also downloaded python 3.5.2. However, my computer for some reason won't use 3.5.2 and my professor told me I needed to download an earlier version to change the project interpreter. Whenever I try to use the earlier version of python for pycharm it says that "the SDK" seems invalid. I don't know what I'm doing wrong and was hoping someone would know what to do. I need to have everything installed and running by Wednesday.