Final answer:
To use an online Microsoft account on a Windows 10 system, go to Settings > Accounts > Your info and select 'Sign in with a Microsoft account instead' to follow the on-screen prompts and complete the process.
Step-by-step explanation:
To switch from using a local user account to an online Microsoft account on a Windows 10 system, you would need to access the User Accounts section in the system settings. Here are the steps to do this: Open the Settings app by clicking on the Start menu and selecting 'Settings' or by pressing the Windows key + I on your keyboard. Within the Settings app, go to Accounts.
Under the Your info or Your account tab, you will find an option that says 'Sign in with a Microsoft account instead'. Click this link. Follow the on-screen prompts to sign in with your Microsoft account or create a new one if you don't already have one. Note that switching to a Microsoft account will allow you to sync settings and files across multiple devices, access the Windows Store for apps, and utilize various other Microsoft services.