If you want to change the Microsoft account you use on your phone, you must first reset your phone to factory settings, which will delete everything you've ever added to your phone. So make sure to back everything up first. See Which apps can I use to sync with my computer? to figure out the best app to use. Note that you'll also need to re-buy anything you bought that requires a Microsoft account to use, including apps, games, and music.
1 Connect your phone to your computer with a USB cable, then back up your pictures, music, and videos.
In the App list, tap Settings Settings icon > About.
2 Tap Reset your phone. If you want to delete the contents of your SD card, tap Erase SD card too.
3 When the warning message appears, make sure you're really ready, then tap Yes > Yes to confirm. Your phone will restore itself to factory settings.
4 When your phone restarts, it will guide you through setup. When you get to the Keep your life in sync screen, tap Sign in, and then follow the instructions to sign in with the account you want to use.