Yes, you can! But, be aware that deleting a project from your portfolio cannot be undone, and it is not possible to delete a project that has been submitted to a hackathon. The reason for this is that hackathons have rules, and those rules include the sponsors having a right to display your submission.
Alternatively, you can also hide your project from your portfolio. Please note, that hiding your project from your portfolio will still allow your project to show in the Project Gallery of hackathons it has been submitted into.
Have more questions? Join us on Discord where the Devpost team is available Mon-Fri from 9-5 ET to assist you!