upgrade to windows 8.1 keeping your local account
Windows 8.1 is designed to be used with a Microsoft account, so we recommend that you give it a try. Simply put, your Microsoft account is the glue that holds together so many useful features of the new Windows. Without one, you won't be able to, for example, automatically sync your settings and documents between PCs, back up your photos to the cloud so you can get to them from anywhere, or see all your contacts from multiple email and social networking accounts together in the People and Mail apps.
But if you're sure you want to use a local account instead, choose Create a new account, then on the new account page, choose Continue using my existing account.