You can rename the Administrator account in Local Security Policy. Type
secpol.msc in the start menu, then navigate to:
Local Policies\Security Options\Accounts: Rename administrator account
The Administrator account is no more or less an administrator than your normal user account which is a member of Administrators. What governs your rights over the system is the local security policy (and NTFS permissions). Assuming you haven't made any changes to your local security policy, you may find a few things that Administrator is granted rights to that Administrators is not. Two particular policies you might be interested in are under
Local Policies\Security Options:
User Account Control: Admin Approval Mode for the Built-in Administrator account
User Account Control: Run all administrators in Admin Approval Mode
If you disable these policies, then UAC is disabled for the Administrator account or Administrators group.
If you believe a member of Administrators is not really a full "administrator", then either you have a security policy in place causing this, or what you're looking to do is to disable UAC, which you can do either through Control Panel (easier and safer) or through Local Security Policy.