Docker Community edition for Mac comes with the following different components


Docker Engine
Docker CLI Client
Docker Compose
Docker Machine

Before upgrading checking the versions

$docker -v

 Docker version 17.09.1-ce, build 19e2cf6

$docker-compose --version

 docker-compose version 1.17.1, build 6d101fb

$docker-machine --version
 docker-machine version 0.13.0, build 9ba6da9

If the Docker is running then from the top menu bar click on the Docker icon and navigate to

Check for upgrade