Open the portfolio you want to delete. At the top right, click the gear icon (Settings) to the left of the time period filter. The Portfolio settings open.
In the portfolio settings, scroll down to the “Danger Zone” section. There you'll find the “Delete portfolio” button.
In the mobile app: In the menu, open “Portfolios” and tap the gear icon at the top right of the portfolio's card. At the very bottom, you'll find “Delete Portfolio”.
If you're in the Overview, the delete option isn't shown, because the Overview can't be deleted. So switch to the respective portfolio to delete one of your portfolios.
When you delete a portfolio, all activities and settings for this portfolio are deleted automatically. The data can't be restored.