You can prevent your iPhone, iPad, or computer from syncing data like photos, contacts, and calendars with iCloud, which is Apple's online storage service. You can turn off iCloud by signing out on your iPhone, iPad, or computer. Keep in mind that disabling this service prevents you from accessing anything you have stored on it until you log back in.
Steps
Method 1 of 3: Turn off iCloud on Mac

Step 1. Open the Apple menu

Click on the Apple logo at the top left of your screen. A drop-down menu will appear.

Step 2. Click System Preferences
This option is at the top of the drop-down menu. Click on it to open the System Preferences window.

Step 3. Select

iCloud.
It's the cloud icon on the left side of the window. The iCloud window will open.

Step 4. Click Logout
This blue button is on the left of the iCloud window.

Step 5. Select the data to keep
Check the box next to each item (for example "Contacts") that you want to save a copy on your Mac.
If you want to delete all data, make sure all the boxes on this page are unchecked

Step 6. Click Keep a Copy
It's the blue button at the bottom of the window. A copy of the selected data will be saved on your Mac and you will be signed out of iCloud.
- You may also be asked to save or remove iCloud passwords on your Mac. If so, click Keep on this Mac to save them or on To delete to remove them.
Method 2 of 3: Turn off iCloud on Windows

Step 1. Open the Start menu

Click on the Windows logo at the bottom left of the screen.

Step 2. Type iCloud
Windows will search for the iCloud app on your computer.

Step 3. Click

iCloud.
This is the cloud-shaped application in the start window. Click on it to open iCloud.

Step 4. Select Logout
This button is located at the bottom left of the iCloud window.
If you're asked to enter your Apple ID when iCloud opens, it means you're already signed out

Step 5. Click Remove from this computer when prompted
This will delete all iCloud data from your computer and sign you out of iCloud.
It may take a few minutes to sign out of iCloud
Method 3 of 3: Turn off iCloud on iPhone or iPad

Step 1. Go to settings

of your device.
Tap the app Settings gray in the form of toothed wheels. Usually found on the home screen.

Step 2. Tap on your Apple ID
This is the name at the top of the screen.

Step 3. Scroll down and tap Sign Out
You will find this option at the bottom of the page.

Step 4. Enter the Apple ID password
Type the password you use to log into your account.

Step 5. Tap Disable
This option is at the bottom of the "Apple ID password" box. Tap it to turn off "Find My iPhone" on the device that uses this iCloud account.

Step 6. Select the data you want to keep on your device
To keep a copy of the data stored in iCloud (e.g. contacts, calendars, etc.), press the white switch

to the right of the items you want to keep. The switch will turn green

To delete all iCloud data from your device, make sure all buttons are in the Off (white) position

Step 7. Tap Sign Out
This option is located at the top right of the screen.

Step 8. Select Logout when prompted
This will confirm your decision to sign out and turn off iCloud on your iPhone or iPad.