Cannot change ownership when trying to establish chown

Good afternoon everyone. I just want to thank all of you for letting me join. I am a noob when it comes to linux and control prompt so please bare with me. 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 /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.