Upgrade OS X Yosemite to El_Capitan

REMARK: Always perform full backup before upgrade

1. Click Apple Menu on top-left corner > Software Update... > Updates > OS X El Capitan Free Upgrade

2. Enter Apple ID. Downloading of 6.19GB

3. Continue

 

4. Agree > Agree 

5. Install

6. Enter MacBook administrator user password. 

7. Installation in progress

8. Restart

9. Close Other Applications...

10. Click Don't sign in > Continue

11. Skip

12. Continue

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