If you have selected to install PostgreSQL then once PostgreSQL has been installed it will install PostGIS.
- Click I Agree to continue with the installation.
- Leave Check the default checked components as above and click Next.
- Click Browse if you wish to change the Destination Folder and click Next.
- Enter the following and click Next:
...
Password: enter the password that you gave the postgres user when you installed PostgreSQL.
Port: 5432
- Leave postgis as the Database Name and click Install.
- Click Yes.
- Click Close to continue with the Astun 3rd Party installation.