How to upgrade django?
You can use the upgraded version after upgrading.
You should check that all your tests pass before deploying :-)
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.