Ahh I see. You have that error.
1. Go to "Security".
2. Scroll down and locate "Encryption". From here you can decrypt the device. This will allow you to also fix "Disabled by administrator", "encryption policy" and/or "credential storage".
NOTE: If your device is encrypted, you will be asked to enter your PIN again and again.
3. Now tap “Device Administrators” and uncheck any box you see.
This should fix the "Disabled by administrator" error.