-U or --upgrade will update listed packages
Example:
$ pip install -U django-simple-captcha
# OR
$ pip install --upgrade django-simple-captcha
pip3
$ pip3 install -U django-simple-captcha
# OR
$ pip3 install --upgrade django-simple-captcha
pip3 with
sudo(to install system-wide, this may be required in some cases)
$ sudo pip3 install -U django-simple-captcha
# OR
$ sudo pip3 install --upgrade django-simple-captcha