How do i remove a Trojan.Brisv.A!inf?

I have a Trojan.Brivs.A!inf on my computer, its high level and says "not safe to remove" it says i need to manually remove it but it wont be removed, how do i remove it? If you know anyways that i dont need to donwload or buy anything that would be great, if i need to please specify where i can get it, thanks.