How do I completely wipe macbook?
To repartition your hard drive (under macOS Sierra)


Open Disk Utility.
Select physical drive (most top level), not any of the partitions you have.
Click Partition button in the top row of buttons.
Select first of your two other partitions and press - button. This shall remove selected partition.
Repeat for the second of your other two partitions.
Select your first partition (where macOS is installed).
Drag resize control (press ⌘ for it to appear) or enter size manually to use all available space and press Apply.




Then follow these steps to prepare your Mac for sale.

What to do before selling or giving away your Mac

When preparing to sell or give away your Mac, you may want to erase some or all files from its hard drive. But first determine whether you should back up your computer and disable certain features and services. These steps show the recommended sequence of actions:


Deauthorize your computer from iTunes, if applicable.
Back up your data using Time Machine or other backup methods.
If you use Find My Mac or other iCloud features on this Mac, complete these steps:


Back up your iCloud content.
Choose Apple Menu () > System Preferences, then click iCloud.
Deselect the Find My Mac checkbox.
Sign out of iCloud. When you sign out of iCloud, you're asked whether you want to remove iCloud data from your Mac. Removing iCloud data in this way makes sure that the data isn't also removed from any of your other devices that are using the same iCloud account.

Sign out of iMessage:


In the Messages app, choose Preferences > Accounts.
Select your iMessage account, then click Sign Out.

Reformat your hard drive and reinstall macOS.
After you reformat your hard drive and reinstall OS X, the computer restarts to a Welcome screen and asks you to choose a country or region. If you want to leave the Mac in an out-of-box state, don't continue with the setup of your system. Instead, press Command-Q to shut down the Mac. When the new owner turns on the Mac, the Setup Assistant will guide them through the setup process.