This is an easy change that can be made in your Photo Manager. Simply select the Portfolio folder that you wish to edit under the Portfolios tab on the left hand side of your screen.
Once you are on the desired Portfolio folder, select the Edit button on the right hand side of the screen.
At this point, a drop-down will appear where you can either check the box labelled Public to make the folder Public or unselect the box to make the folder Private. Once you have make the necessary changes, make sure you hit Save in the top right hand corner!