Tap the hamburger icon (top-left) or swipe from the left edge on the portfolio screen to bring up the 'Portfolios' menu. In minimized header mode, tap on the 3 dots in the right top corner and select 'Switch Portfolio' or 'Add New Portfolio' to bring up the 'Portfolios' menu.
Once the portfolios menu is open - tap 'Edit' and then on the red delete icon (red circle with white dash) to completely remove a portfolio. The app will ask for your confirmation before deleting. Please note that this action is irreversible! The portfolio cannot be recovered EVEN IF you have a recovery code because the recovery code is dynamic and it is not a snapshot.