To add Python to the Windows Path, follow these steps:
1. Start the Run box and enter sysdm.cpl
2. In the System Properties window go to the Advanced tab and
click the Environment Variables button
3. In the System variable window, find the Path variable and
click Edit
4. Position your cursor at the end of the Variable value line
and add the path to the python.exe file, preceeded with
the semicolon character (;)
setx PATH "%PATH%;C:Python34Scripts"
Simply add this path to your PYTHONPATH environment variable.
To do this, go to Control Panel / System / Advanced / Environment variable,
and in the "User variables" sections, check if you already have PYTHONPATH.
If yes, select it and click "Edit", if not, click "New" to add it.
Paths in PYTHONPATH should be separated with ";".
Either manually change it by doing the steps for the answer by skilliboi.
Or you can reinstall python and when you do that, make sure to tick the box that says:
Add python to PATH (or something like that)