Oftentimes, when you no longer use a device, you might wish to remove it from your iCloud account - to save space, to allow a repairer to diagnose the device, etc. Follow the instructions below to remove a device from your iCloud account remotely.
Visit https://www.icloud.com/ and sign in to access your iCloud.
Scroll down the page until you locate the "Find My" app icon, as shown below:
At the top of the next page, click the "All Devices" drop-down menu, and locate the device you wish to remove from the list. The device must be offline to remove.
Select the "Remove from Account" option, and confirm your choice.
If the only option given is to "Erase Device", DO NOT SELECT. The device must be offline to remove it without erasing all content on the device.
You have successfully removed the device from your iCloud account. You may also need to remove the device from your Apple ID, instructions which can be found here.