Firstly, verify which version you have installed already:

servicecatalog-puppet version

If this errors, check you have activated your virtualenv.

Then you are ready to install the version you want:

pip install aws-service-catalog-puppet==<version>

If you want to upgrade to the latest you can run:

pip install --upgrade aws-service-catalog-puppet

Once you have completed the upgrade you will have to bootstrap your install again:

servicecatalog-puppet bootstrap

And finally, you can verify the upgrade has worked by running version again:

servicecatalog-puppet version