In addition to Aura's advice...
It sounds VERY strange that you now have the paid, Premium MBAM (Malwarebytes Anti-Malware) if you never paid for a license.
Even with the new licensing system, this ought not to be possible.
There is a "1 Trial per PC per Program Version" feature for the consumer version.
So, if you have recently updated from a version BEFORE 2.1.8 to version 2.1.8, then it may be that you have a new Trial for the 2.1.8 build???
If your dashboard ribbon at the top really does say "Premium" (not "Trial") and if you see full account information in that window, then perhaps someone else with access to your computer has purchased a Premium MBAM license and has activated it? (In that case, you might see BOTH an "ID" and a "Key" in the display.)
The other possibility is that you may have had a "problem" license (perhaps purchased inadvertently from an unofficial source or seller) that was automatically migrated to a new, replacement license? (If that's the explanation, there would be ONLY a "Key", and no "ID" in the display.)
In any event, as Aura mentioned, MBAM Premium is NOT an anti-virus and does not replace one.
To the contrary it is specifically designed to provide realtime, layered protection alongside your AV, to protect against zero-hour and zero-day threats often missed by the AV.
There is no need to deactivate MBAM Premium to change it back to the manual, on-demand scanner.
>>If you have performance issues on a slow system, please post back and we'll explain how to set mutual exclusions between ESET and MBAM.