On your dashboard click Places and then select Portfolios on the dropdown.
Then search for the Portfolio name in the Search bar.
Once you found the portfolio name, navigate to the right side of the page, click the ellipses icon, and select Delete Portfolio.
A pop-up message will appear, and to confirm action click OK.
Deleting a portfolio will not affect the status of the properties included in it. The purpose of deleting a portfolio is to ungroup the properties.