Avast Security on my MacBook Air.

I've installed a free version of Avast Premium Security on my Mac and the 60 days is nearly up.

Im getting slightly doom-laden popups about not taking the paid version. I'm new to Macs having Dell laptops until last December. I have heard a lot about Apple and their inbuilt security system but unsure whether to trust in that. Any advice would be gratefully received.

Thanks, Paul.