In order to remove an iCloud from a device please follow the steps below:

STEP 1 - Sign in to with your Apple ID and go to Find My iPhone.


Or if you have signed in press Find my iPhone.



STEP 2 - Click All Devices at the top of the screen and select the device that you want to remove from iCloud.



STEP 3 - Click Erase [device]. Select Next until the device is erased. 



STEP 4 - Click Remove from Account.



Now the iCloud account should no longer be associated with the device.