How can I remove one ios devise from icloud and keep its data

Are you going to sell the old one? If yes, it will be erased and whatever you erase from a device will be erased in iCloud as well. But, if you moved everything to your new device, then it will still be on iCloud of course.

babowa wrote:

Are you going to sell the old one? If yes, it will be erased and whatever you erase from a device will be erased in iCloud as well. But, if you moved everything to your new device, then it will still be on iCloud of course.

Yes. if you remove the device from iCloud before erasing anything on it, everything will be kept in iCloud and the device if you select the option to do so.

Things would only be erased from iCloud if you manually erase things on the device before removing it from iCloud.

Simply removing the device from iCloud, does not erase anything on the device nor on iCloud.

Follow the steps here to remove it from iCloud so all its data is kept on iCloud: What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

You can then specifically choose to leave data on the device, or simply wipe it clean once you are done.

Any data you backup to iCloud will remain there until you delete it. Removing a device does just that.