Assuming that your PC is in "Tablet Mode" and you are running PicCollage on a landscape screen.
Here are the steps for creating a portrait collage.
a) You need to exit "Tablet Mode".
On a desktop PC, right-click at the lower right corner of the task bar and select "Open Action Center".
On a Win tablet, swipe in from the right into the screen to open the same Action Center.
On the Action Center sliding menu, look for a "Tablet Mode" button and turn it off.
b) Select "Grid" or "Freeform". You can set collage size in these two modes. In "Templates" mode, the size of your collage is set by the template you select.
c) Resize the window to the desired shape. You can resize the window by dragging on any window corner.
Note: It is important that you resize the window BEFORE adding any content to the collage. As soon as you put one photo in the collage, the collage size is set; further resizing will not change the shape of the collage any more. Similarly, you cannot change the shape of an existing collage by resizing the window. You can only set the shape of a new collage.
Can also refer to the animation and screenshot in our blog: https://blog.pic-collage.com/2016/09/16/how-to-make-a-portrait-collage-on-a-windows-tablet-or-computer/