"Refurbish" doesn't have a standard definition in the electronics industry. Apple describes refurbished products as having defective parts replaced, cleaned, fully tested and repackaged with all originally-included cables and documentation. Apple sells refurbished MacBooks that fit this description. To refurbish a MacBook yourself -- for resale or for personal use -- minimally involves renewing it to its factory-fresh state. You can also take the opportunity to upgrade certain components of your MacBook.
Back up the data on your MacBook. Use an external hard drive or flash-based memory device to save your important personal documents and media.
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Take an inventory of malfunctioning and missing parts and order replacements. Use either OEM or a reputable third-party parts supplier. If you want to upgrade a component, check the technical support section of Apple's website to find out which parts are compatible with your MacBook.
Replace malfunctioning and missing parts with the new parts. For detailed instructions specific to your MacBook model, consult Apple's technical support site, where you will find all available user guides and service manuals.
Restore the operating system using your OS X Install discs.
Wipe down the case, keyboard and screen. Use either water or very mild cleaning agents intended for laptops.
Test your refurbished MacBook by launching the Apple Hardware Test. To run the Apple Hardware Test, boot your computer and immediately press and hold the "D" key. When prompted, select "Perform extended testing" from the menu. When testing is complete the results display and you can reboot your MacBook.