If you want to submit another work of yours, or want to start fresh with what you had already entered: It's easy! There's a button in the top right corner, labeled "Manage my projects"
Just click "Begin new project" there and you can start again. No worries: You can always come back to your previous projects and work on those by clicking "Manage projects". However, this works only until you have submitted them for publication at the last step.