What to do if I’m trying to delete files but it won’t, like i get error messages/”cannot delete file”?

I’m trying to upgrade my antivirus, and when im trying to click the
upgrade, it wont do and get errors, and the uninstall isn’t working as well,
so I also tried to manually delete the folder, but it won’t delete as well.
I also tried downloading the new version of that anti-virus, thinking that
maybe it could upgrade and overwrite the old one, but also won’t, the old
one should be removed, how do i do that if I cant get it done?