Just press and hold the power button on your Mac until it turns off. If you're selling, giving away, or trading-in your Mac and want to leave it in an out-of-box state, don't use the setup assistant or your previously connected Bluetooth devices, if any.

After restart, a setup assistant guides you through the setup process, as if you're setting up your Mac for the first time.

Go to Apple Menu and choose About This Mac.

After joining a network, your Mac activates. Empty your Trash regularly and if you keep forgetting enable Apples automatic Trash cleanup.

To select a Wi-Fi network, use the Wi-Fi menu in the upper-right corner of the screen.

You might be asked to select a Wi-Fi network or attach a network cable.

When reconnecting to a Bluetooth keyboard, you're asked to choose a language. If the accessory doesn't connect within 30 seconds, turn the accessory off and back on. If it needs to reconnect to a Bluetooth accessory such as a keyboard or mouse, you might be asked to turn on the accessory. Your Mac restarts and shows a black screen or progress bar.The second option allows you to delete the heaviest files, like movies and apps. Store in iCloud lets you transfer all your data to cloud storage and reclaim some GBs on your Mac. In the window that appears, you can see some useful suggestions. Click Erase All Content & Settings to confirm that you want to proceed. And, finally, it’s time to think about your RAM memory as well. Go to the Apple menu and select About This Mac > More Info.If you're asked to sign out of Apple ID, enter your Apple ID password and click Continue.Click Continue to allow your settings, media, data, and the other listed items to be removed.Or click Continue to proceed without making a new backup. This is the ultimate way to clear out the RAM. If you're asked to back up your Mac before resetting it, you can open Time Machine and back up to an external storage device. This should help a lot because it shuts down all ofyour open applications and documents.Enter the password that you use to log in to your Mac, then click OK. An erase assistant asks you to sign in with your administrator credentials.After choosing Erase All Content and Settings, follow these steps to continue:

How to clear memory on macbook air