I cloud space

You can change the amount of storage by selecting a new plan right from your iPhone, iPad, iPod, Mac, or PC (for example, a 5 GB plan to replace a 200 GB plan). The downgrade will take effect after your current monthly or annual subscription ends.

iOS

1. Go to Settings ➔ Apple ID(Top) ➔ iCloud ➔ Storage ➔ Manage Storage.  
2. Tap Change Storage Plan.
3. Tap Downgrade Options and enter your Apple ID password.
4. Choose a different plan to use when your current storage plan expires.
5. Tap Done.

After you downgrade to the free plan, your settings won't change, they'll stay as they are until the end of your payment period when it will change.

Yes, it will change when your current payment period expires.