Do you mean your saved programs/progress or your leaderboard scores?
For your code and whatnot, it’s stored in HTML Local Storage in the browser (on your computer). Deleting it is different by browser, but for Chrome open dev tools with F12, go the Application tab, and delete the entries that start with “sic1_”. Clearing browser history also deletes it, but that also deletes all your browser history, which you probably don’t want.
For deleting leaderboard data, I haven’t published the instructions yet, but the instructions will be in the next update (coming next weekend). If that’s what you’re looking for, let me know which browser you’re using and I can try and give you instructions that will work on the current version (there’s no UI for this in the current version).