How do I change the format and use A3

I want to use Landscape format
I want to set it to A3 for printing that size
I want to upload multiple [identical] images

Select Format>Page for a dialogue allowing you to set Format to A3 and Orientation to Landscape. If necessary, see your printer instructions for advice on how to set it to use A3 paper.

This works with Windows 7/LO 6.0.6 and I have not heard of any difficulty with other OSs and versions.