How to turn off Android Device Manager on the web
The Options box gives you a list of devices linked with your google account to select from. If you just had only one device, there might not be any drop-down Options box. You should be able to view/manage the devices by going to 
https://play.google.com/settings



Some more info that might help: (Source )

Switch Android Device Manager on or off

Before you can use Android Device Manager, you need to make sure it's turned on and that your device is associated with your Google Account. If you have a tablet with more than one user, only the tablet owner can control this setting.


Find Google Settings in one of these places (depending on your device):


A separate app called Google Settings 
In your main Settings app, scroll down and touch Google

Touch Security.
Under "Android Device Manager," switch Remotely locate this device and Allow remote lock and factory reset on or off.