Look into the image. Simply change the URL from "changeme.html" to the answer.
Don't forget to add ".html" at the end. IMPORTANT information about answer submissions: all answers will be written in lowercase, using only a-z or 0-9 characters.
No spaces are included in answers; if your answer is "right triangle," then you would input righttriangle.html.
Username/password levels are an exception (you will see).