There is TROJAN HORSE virus in my laptop

Question

there is trojan horse virus in my laptop. i ve a symantec norton 2004 antivirus. everytime i update my antivirus, there's some process happening n it comes again unable to h**l the virus.... it got detected in 3 locations in the laptop. i dun know wat shud b done to treat this virus n procedures to be followed for its removal.