Chown: changing ownership of '/opt/heimdall/ <file> : operation not permitted

So I'm struggling with this.I am currently trying to install Heimdall-flash to my chromebook and I'm afraid that I've made a mistake. I successfully cloned /opt/heimdall/ but I can't seem to get my chown-R www-data:www-data /opt/heimdall/ to change ownership. I have struggled with this for several days. I know there is a method of changing ownership but I've just begun to learn to understand all the commands. Please any help would be greatly appreciated. Thanks and have a great day. I have tried root and honestly I dont have all the commands or issuing of them down yet. So will you please breakdown the commands so I will understand the whole command line start to finish