How to remove an app with active device admin enabled on Android?

Go to SETTINGS->Location and Security-> Device Administrator and deselect the admin which you want to uninstall.

Now uninstall the application. If it still says you need to deactivate the application before uninstalling, you may need to Force Stop the application before uninstalling.

You could also create a new DevicePolicyManager and then use removeAdmin(adminReceiver) from an onClickListener of a button in your app

//set the onClickListener here
{
   ComponentName devAdminReceiver = new ComponentName(context, deviceAdminReceiver.class);
   DevicePolicyManager dpm = (DevicePolicyManager)context.getSystemService(Context.DEVICE_POLICY_SERVICE);
   dpm.removeActiveAdmin(devAdminReceiver);
}

And then you can uninstall