The way is
pip install <package_name> --upgrade
or in short
pip install <package_name> -U
Using sudo will ask to enter your root password to confirm the action, but although common, is considered unsafe.
If you do not have a root password (if you are not the admin) you should probably work with virtualenv.
You can also use the user flag to install it on this user only.
pip install <package_name> --upgrade --user