I answer you with another question, why do you want to uninstall a free security system developed by the same company that created the operating system?

If what you want is to remove windows defender you can go to services and disable services related to windows defender, on the other hand if you install an antivirus on windows 10 automatically disables windows defender,

I still think it makes no sense, but there you have the answers, googling you will have step by step guides on how to do it,

I think you can uninstall windows defender if you use third party software,