Leftover files when uninstalling Anti-Virus – do they need to be removed when using newly installed Anti-Virus?

I recently purchased a new laptop. I have two questions.

  1. When I did the original setup, I chose the option "No" when it asked if I wanted to download an anti-virus program. However, even though I chose No, it still downloaded McAfee. Is this typical?

  2. I’ve uninstalled McAfee and downloaded a new Anti-Virus program. However, I am now noticing there are a number of folders with mcafee still saved – under Windows/System32 folder as well as AppData folder. Would this cause issues with the New Antivirus running, given there are still some files/folders from the old one on the PC? Is it safe to delete these?

Thanks very much!