You can either tap the hamburger icon (top left) or swipe in from the left edge to bring up the options to switch, rename or delete portfolios.
To switch, simply scroll and tap on the portfolio of your choice.
To rename, tap the 'edit' icon (next to "My Portfolios") and then the pencil icon (A) to type in a new name for the portfolio.
To delete, tap the 'edit' icon (next to "My Portfolios") and then on the red delete icon (B) to completely remove a portfolio. Please note that this action is irreversible!