How to downgrade or cancel your iCloud+ plan on your iPhone, iPad, or iPod touch
1. Open the Settings app.
2. Tap your name.
3. Tap iCloud.
4. Tap Manage Account Storage or Manage Storage.
5. Tap Change Storage Plan
6. Tap Downgrade Options and enter your Apple ID password
7. Choose a different plan. To downgrade your plan, choose a new storage amount. To cancel iCloud+, choose the free 5GB plan or choose None.
8. Tap Done. If you can't tap Done, make sure that you're signed in with the same Apple ID that you use for your iCloud+ plan. You can also try following these steps on a different device. If you still need help,
contact Apple Support: https://getsupport.apple.com/.
Note:
Your storage space will be downgraded after the end of the current monthly or annual subscription. If you are currently using more than 5GB iCloud space, we advise you to downgrade prudently.