Upgrade OS X El Capitan to macOS Sierra

REMARK: Always perform full backup before upgrade

1. App Store > Search 'macOS Sierra'.

2. Click DOWNLOAD button under 'macOS Sierra'. Wait for downloading of 4.95GB to complete.

3. Launchpad > Click 'Install macOS Sierra'.

4. Click 'Continue'.

5. Click 'Agree'.

6. Click 'Agree'.

7. Click 'Install'.

8. Enter MacBook administrator user password > Click 'Add Helper'.

9. Installation in progress.

10. Click 'Restart'.

11. Click 'Close Other Applications...'.

12. MacBook will be restarted and installation in progress.

13. Select 'Don't sign in' > Click 'Continue'.

14. Uncheck 'Enable Siri on this Mac' > Click 'Continue'.

15. To verify, click on 'Apple' icon > About This Mac

URL: https://support.apple.com/en-us/HT201475