This wikiHow teaches you how to remove and reinstall the operating system on a Windows or Mac computer. Doing so is typically a response to a corrupt or infected operating system. Before re-imaging your computer, you should back up your data to an external hard drive.
StepsMethod 1Method 1 of 2:On Windows
1Open Start 
. Click the Windows logo in the bottom-left corner of the screen.
2Open Settings 
. Click the gear-shaped icon in the lower-left side of the Start window.
3Click 
Update & Security. This icon is near the bottom of the Settings window.
4Click the Recovery tab. It’s on the left side of the window.
5Click Get started. You’ll find this option below the “Reset this PC” heading near the top of the page.
6Click Remove everything when prompted. It’s at the top of the pop-up window.
7Click Remove files and clean the drive. This option will completely erase your computer’s hard drive and then reinstall Windows 10 on it.XYou may see a warning about not being able to roll back to a previous version of Windows here. If so, click Next before continuing.
8Click Reset when prompted. Your computer will begin resetting itself.
9Wait for Windows to finish resetting. The reset process can take several hours to complete, so just make sure that the computer is plugged into a reliable power source to ensure that it doesn’t shut down.
10Click Continue when prompted. Once your computer finishes resetting, you’ll see this at the top of the page. Clicking it will take you to the setup page.
11Follow the on-screen prompts. You’ll select a language, connect to a Wi-Fi network, and perform other setup tasks to complete the Windows 10 reinstallation.Method 2Method 2 of 2:On Mac
1Open the Apple menu 
. Click the Apple logo in the top-left corner of the screen. A drop-down menu will appear.
2Click Restart…. It’s near the bottom of the drop-down menu.
3Click Restart when prompted. Your Mac will begin to restart.
4Place your Mac in recovery mode. Immediately after clicking Restart, press and hold the ⌘ Command key and the R key simultaneously until greeted by the “Utilities” window.
5Select Disk Utility. It’s the grey hard drive-shaped icon in the main window.
6Click Continue. This is in the bottom-right corner of the window.
7Select your Mac’s hard drive. On the left side of the window, click the hard drive on which your Mac’s operating system is installed.
8Click Erase. It’s a tab at the top of the window. A pop-up window will appear.
9Click the “Format” drop-down box. You’ll find this on the right side of the page. Doing so prompts a drop-down menu.
10Click Mac OS Extended. It’s in the drop-down menu.
11Click Erase. This is in the bottom-right corner of the window.
12Wait for your Mac’s hard drive to finish erasing. The erasing process will take some time, so just make sure that your Mac is plugged in and charging to prevent it from accidentally dying.
13Click Done when prompted. Doing so completes the erasing process.
14Click Disk Utility. This menu item is in the top-left side of the screen.
15Click Quit Disk Utility. It’s at the bottom of the Disk Utility drop-down menu. Doing so returns you to the main Recovery window.
16Select Reinstall macOS, then click Continue. MacOS Sierra will begin reinstalling itself on your hard drive.17Follow the on-screen prompts. Once MacOS Sierra has been reinstalled, you can proceed with setting up your Mac (e.g., choosing a language and connecting to Wi-Fi).
