Steps to rename administrator account
1. Open the Charms bar by moving your mouse pointer over the right corner of your screen. Alternatively you may press Windows key + C on Start screen to open Charms bar. Then select Search
2. Next, type ‘secpol.msc’ into the search box and click the search button. Then click on the secpol.msc icon on the left side of the pane.
3. Next, expand “Local Policies” by clicking on it’s expand icon.
4. Next, Under Local Policies on the left pane, click on the Security Options. And on the right pane, right click on the Accounts: Rename administrator account and select Properties.
5. Finally, rename the default administrator account name and then click on the OK button. That are the complete steps to rename the Windows 8 administrator account.