The Nike+ SportWatch GPS can only be linked to one Nike+ account at a time. The SportWatch is not configured for use by more than one runner.
You can transfer the SportWatch from one person to another user by linking it to a different Nike+ account. To do so, first complete a SportWatch factory reset in Nike+ Connect.
After resetting, you will be prompted to sign in to Nike+ when you upload your first workout. Enter the username and password of the Nike+ account you wish to link to the device.