To download the installer file, visit the PostgreSQL official website (https://www.postgresql.org/) and then perform the following steps:

1. Once you are in the home page of the PostgreSQL official website, go to the Download page.
2. On this page, you will see the options for various operating systems. Click on Windows.
3. On the Windows download page, click on Download the installer under the Interactive installer by EnterpriseDB section.
4. Once you click there, it will redirect you to another page where you will be given the option to select the specific operating system and the version of PostgreSQL. Then, hit the DOWNLOAD NOW button.

The installer will be downloaded onto your computer, and you are ready to install it.