You may want to do this to run Linux or Windows on your Chromebook. Before proceeding please make sure you made a backup of all of your data on your Chromebook. This can be done by either using the built-in free Google Drive cloud storage or an external media device like a hard drive or USB stick. This process is quite hard and shouldn't be done by people who have no idea what they are doing. If you don't want to open up your Chromebook, risk electrocuting the board or do anything else stupid you shouldn't follow this guide. I warned you.
Making sure your Chromebook is supported
To find out which Chromebooks are supported head over to this site which explains which Chromebooks are supported and which method is required to remove write-protect and enable full BIOS flashing (essentially allowing you to install Windows and not just Linux distributions).
Creating a restore media in case you accidentally nuked your Chromebook's operating system
Just download the Chrome OS recovery tool from the Chrome Web Store and follow the on-screen instructions. Make sure you create the right restore media for your specific device model or things will go horribly wrong.
Removing the write-protect screw and enabling developer mode
Some Chromebooks require to remove the write-protect screw to allow a full BIOS flash. This is a screw inside your Chromebook and is usually screwed on the motherboard. Please do some research on your specific Chromebook model. Make sure you don't damage any cables inside your Chromebook, sneeze on it or electrocute the whole board by not grounding yourself first. If the hard part was done we can continue doing the easy part. In case you want to do games on your Chromebook or install Windows you should also consider buying a larger SSD for your Chromebook. Make sure the SSD fits into your Chromebook, some might look like the right one, but they do have different sizes and connectors which would make them incompatible. Buying them from Amazon is a good idea (except if you care for Amazon worker's health), because you can send them back without giving a plausible reason in case you bought the wrong one. If you inserted a new SSD into your Chromebook make sure you reinstall the operating system with the restore media you created earlier by booting it up and plugging it in. Afterwards follow the on-screen instructions and make sure your Chromebook is plugged into an AC power adapter. If you have done all that and logged into your Google account and let the device sync your whole profile we can continue to the next step which is finally enabling developer mode. For this press the Esc-Reload and Power keys simoultanously (the power key might be on the side or something else on some Chromebook models) and you should see a warning that your operating system is missing or damaged. You can ignore this and press Ctrl-D. Follow the on-screen instructions to enable developer mode. Now every time you boot you can either wait 30 seconds and let it beep two times to continue normal booting or press Ctrl-D to skip the scary warning screen.
Installing the firmware
Open a terminal by pressing Ctrl-Alt-T and enter the following
shell sudo su - cd curl -LO https://mrchromebox.tech/firmware-util.sh sudo bash firmware-util.sh
And you should see a screen that looks something like this
On this screen you can decide to either update the RW_LEGACY slot of your Chromebook which only enables you to install Linux or flash the full firmware to enable installing Windows. If you plan to restore your firmware on your Chromebook and put Chrome OS back on it when you installed the full firmware, make sure you back up your firmware and keep it safe. Losing or not backing up your firmware will require you to buy a new Chromebook to dump the firmware from. Also make sure you don't interrupt the process or choose the wrong Chromebook model. If you do this you can irreversibly damage your Chromebook (bricking).