While you can reset your code on individual exercises within a lesson, there is no way to reset all of your courses at once without deleting your account.
Depending on the course that you're taking, you can reset the code in that exercise by following one of these methods.
Click the this "Reset Course" button here:
Or here, depending on the course you're taking:
Please note that these methods will only reset a single exercise within a unit and not the full course itself.