If you want the free version of Malwarebyte's Anti-Malware you need to click the GREY 'Download' button here:
https://www.malwarebytes.org/free/
(For the paid version, click the GREEN 'Upgrade' button).
If you want to get that free version without also taking a free trial of the 'PRO' version, simply double-click on the file you downloaded to start the installation process. At one point during that process you'll see a screen with three options pre-ticked. One of them relates to installing the 'PRO' trial; simply click to remove that tick and then proceed. (You can leave the other ticks in place).