Is it necessary to uninstall Norton or any other antivirus program prior to installing a different one?
Yes run only one antivirus program, otherwise they conflict with each other. You can run multiple spyware detection and removal programs such as SpyBot Search & Destroy and Malwarebytes’ Anti-Malware. Norton and McAfee do not uninstall completely. You will need to download and run the Norton Removal Tool or the McAfee Removal Tool. You do not have to uninstall Norton or McAfee before running this tool, it will perform the complete uninstall for you in one operation.