Hi Melinda thanks for reaching out. You can choose to print in landscape or portrait mode in the print settings (see screenshot).

If you want to split the diagram up over several pages when printing I would suggest splitting the diagram up onto different tabs in Lucidchart and then print those. You can do this by creating new tabs as described in this help center article and then copying the sections of the content you want to print separately onto different tabs. 

Alternatively if the content in your document is occupying more than one tile selecting “Divide by Page Tiles” each tile will be printed on a separate page. You can learn more about the page tiles in this help center article.

Hope this helps.