Look at the extensions tab from the settings menu, look for any unwanted extensions that may be allowing ads to pop up. Delete them. Close and Re-open Chrome. Check if they're still there.
If not, good for you
But if they are still lingering in your PC, then go back to the extensions tab, select " developer mode " , and try to find where the extensions are from. You may have to delete the unwanted extension directly from the Chrome File.