How to switch iCloud accounts on a mobile device
To switch iCloud account, all you must do is go to Settings>iCloud, hit "Delete Account",
then use the correct ID to sign back in.
What this does is delete the iCloud data from the device, but it's still stored in the iCloud anyway
So when you sign back into the account, all the data will reappear when it syncs.
If you're worried about losing photos, you need to save them to your camera-roll by the way! That;s a mistake I made :(