Open a layout program (MS Word, MS PPT, Google Slides, etc)

Set up the page with images in order and requested size

(Full, 1/2 page, 1/4 page)

Once images are in the desired layout, save the page as a PDF.

Save each PDF individually

Open Showgram

Create a new page for each PDF you want to add

Name the page

Save the PDF as a PNG

Upload one PNG per page

Save