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Good News is, your Mac can handle the latest 10.12 Sierra.
Follow the steps below to upgrade the OS X.
Click on the Apple icon and App Store. This will bring App Store. Click Updates tab. You will see macOS Sierra there with FREE UPGRADE button. Click Free Upgrade and enter your Apple ID and password.
This will download the update. It may take a few hours to download. Once the download is completed, it will bring the OS X Installer. Follow the onscreen instructions to install it. It may take up to 3 hours to install the upgrade.
If you have any questions or would like any additional information, please don't hesitate to ask.
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You're most welcome Phil. Remember this is a major upgrade process so it will take some time, so make sure you have enough time before starting the upgrade. The upgrade process shouldn't be interrupted.
If you have any questions or would like any additional information, please don't hesitate to ask.If you are satisfied with my service, please rate me as Excellent Service ( 5 stars) and click Submit at the top. Then only I will get credit for helping you. Bonuses and High marks on the surveys you get from JustAnswer are greatly appreciated.Best Regards,Ashik
Apple ID would be your email address you registered with Apple.
If you don't remember your Apple ID, then you can find it fromhere --> https://iforgot.apple.com/password/verify/appleid#!§ion=appleid
If you don't remember the password, then you have to reset the password. You can reset it from here (go to this website from your computer) --> https://iforgot.apple.com/
Go to the above website. Choose " I want to reset password". Use the "Get an Email" method to reset the Apple ID. Apple will send the reset instructions to the recovery email you setup with your Apple ID. It would be your email registered with Apple, like Gmail, Yahoo etc. Open your email and you will see the email from Apple. Open it and follow the instructions to reset the password.
If that didn't work, then go to this site again --> https://iforgot.apple.com/
This time use the "Answer Security Questions" and answer the security questions there to reset your password. Then upgrade.