how do I change my current iCloud email to another one without losing any of my contacts, notes etc.?

i have a new email that I want to use for my iCloud account but I don't know how to safely change it without losing any of my contacts and data. I recently set up my mum's new iPhone and she didn't want the iCloud email that she has and i deleted the account. it got rid of everything and luckily, we restored the phone to last backup on her old iPhone and we got everything back. I don't want this happening. any help is appreciated 🙂