How to upgrade django?
pip3 install django -U
this will uninstall django, and then install the latest version of django.

pip3 is if you use python3.
-U is shortcut for --upgrade
My project was running on Django 1.5.4 and I wanted to upgrade it. I did pip install -U -I django and now pip freeze shows Django 1.6.5 (clearly django has upgraded, I'm in virtualenv) but my project is still using Django 1.5.4. How can I use the upgraded version? 
UPDATE: Thanks for your comments. I tried everything but unfortunately nothing worked and I had to re-deploy the app.
Hope someone explains why this happened.