Running two antivirus products on the same computer can degrade performance and cause system instability. It is important that any previously installed antivirus software is uninstalled from your system before installing a new security product. Typical uninstallation using the Windows removal tool (Add/Remove Programs) is often insufficient.
1. Click the link associated with the antivirus software currently installed on your system and follow the prompts or instructions on the website.
2. After uninstallation is complete, you will need to restart your computer. You may then proceed with installing your new security product.
From ESET Knowledgebase