Can I replace Office 365 with Office 2019?
Can I replace my existing Office 365 with Office 2019 on my computer using Windows 10? If so, how do I do it?
You may certainly switch from Office 365 to Office 2019.
You will need to uninstall Office 365 from Control Panel > Programs and Features, then install Office 2019.
However, don't expect your Office 365 serial key to work for activating Office 2019. A separate serial key must be bought for Office 2019.