When Malwarebytes installs, you are given a free 14-day trial of their Premium Protection.
I like to run the Real-Time Protection at least once before turning it off but you can let it run the full 14 days and it will tell you your trial is over and that it is time to buy it. I wrote in a previous article How To Turn Off Malwarebytes Free Trial. If you did not turn it off, you will see the following when the trial period ends:
You do not have to upgrade; just choose “I don’t need real-time protection” and click OK. Your account will be set to the free version.
As you can see in the above image, I chose the free option and all the premium options were turned off.
Remember that the free version does not run by itself. You need to run it often to be sure things are cleaned out.