I had the opportunity recently to take a couple of old Windows laptops and make them into Chromebooks using the free (I love free) ChromeOS Flex. Using the directions at the link below, you start by writing ChromeOS Flex to a flash drive using the Chromebook Recovery Utility, an extension you add to your Google Chrome browser. That flash drive is then inserted into the target laptop and booted, and finding how to get the laptop to boot from it was the tricky part. On an HP, I found that tapping "F2" as the machine powered up worked, but on the Dell it took the "Esc" key. After getting past that, the rest was easy.