Antivirus programs can conflict with each other and cause problems, which is why it is recommended that you only have one installed at a time. Apart from the fact that two security programs do not provide twice the security. It does not work that way.
Although all programs have uninstallers bundled with them, they often do not remove everything and sometimes they leave behind traces, program fragments and settings that can cause problems with new software. It is best to remove every last trace of an antivirus program before the new one is installed.
Sometimes uninstallers or the software they are trying to uninstall can become corrupted. This can also cause problems and a security program might be partially removed, but parts remain.
If an application’s uninstaller is not sufficient, what is?
One option is to use an uninstaller utility and there are general tools and ones that are specific to security software.
Many security software developers provide utilities that remove all traces of a program, such as Avast and AVG. They often do a more thorough job than the regular uninstaller that is run from Programs and Features in the Control Panel.
Rather than list all the removal tools here, go to this ESET Knowledgebase page and scroll down. There are links to removal tools for many popular security programs. Find your program, click the link and download the uninstaller or clean-up tool.
Also on that ESET Knowledgebase page is ESET AV Remover. It claims to be able to remove almost all antivirus software and it could be useful, although in my test it wasn’t.
After scanning the computer for antivirus software, it found nothing.
Maybe Panda free antivirus is the one program it does not uninstall or perhaps the utility is not compatible with Windows 10. Don’t let this one failure put you off because it could be a useful tool.
Another option is to use an uninstaller utility and IObit Uninstaller is a favourite one. It is free and it works well. It runs the program’s uninstaller and then afterwards it scans the disk and registry for left-over items that were not removed. It then cleans them up.
Once you have a clean computer, you can download and install new or updated security software. Almost all antivirus programs are better than Windows Defender that comes with Windows, so it is almost impossible not to increase the security.