Please check the below links, Let us know if that helps.
Design a print as a "Custom Package"
Add cells to Package, adjust cell sizes by selecting cell and dragging corners.
Drag Images into cells.
Click on the [ + ] on the Template Browser to save your design as a template-
You can modify cells by selecting a cell and a right-click gives options-
Move images within a cell (If the aspect ratio is not the same) by holding down the CTRL key as you drag/push the image within the cell. (The cursor changes to a hand icon)