Although no harm should come to your computer by having competing antivirus programs on it, there’s no benefit to having multiple ones, especially if you are paying for them. If you have acquired a new antivirus program to replace an existing one, the best option is to uninstall the existing antivirus program from your computer before installing the new antivirus program. Once installed, run the new program in its entirety to make sure your computer is virus-free. Check to make sure it is up to date as well.