How can I upgrade Numpy in just one version of Python?
Extending the first answer by JCutrer, after installing numpy on the specified version, you need to run the python.exe interpreter of the specified version. 
So, assuming  you did
c:\python27\Scripts\pip.exe install --upgrade numpy, the libraries have been installed for python27, now you can run python from the below path, or set this path as interpreter in your IDE. 
c:\python27\bin\python27.exe (or python.exe)
I am trying to get OpenCV working, but the issue with this is that my Python27 Numpp version is too old. Every time I write "install --upgrade numpy", I am told that Numpy is already up to date in C:Python37. How can I update Numpy in C:Python27 rather than 37? Any help would be much appreciated.