If you keep avoiding the update it is more than likely that you will be regularly pestered by the 'pop-up', The supposed 'better' version is free but does install with a trial of the Premium version. Originally the trial was for a month but I think you will find that it has been reduced to a fortnight. However, you can cancel the trial immediately after it is overlayed onto your present free version.
Turning off Malwarebytes Premium Trial......Open Malwarebytes, click on settings > my account > deactivate premium trial......... A notice will then appear to let you know that cancelling the Trial will revert your account to Free and you'll loose Premium features.........Which , in my opinion, are Not worth paying for as mentioned by O_G.
Incidentally, you have Windows Defender inbuilt into Windows 10 and a lot of folk, including myself, are happy enough with it as the Anti Virus programme which is needed alongside Malwarebytes.
Hans.