1. Here's how
The highest render resolution in Lumion is Poster resolution (7680x4320 pixels).
1.1: If you need to render an image that exceeds this resolution, make sure to render the image in an uncompressed file format (e.g. .PNG or .BMP) and then consider using a dedicated image re-scaling tool such as SmillaEnlarger or BenVista PhotoZoom Pro to re-scale the Poster image to the desired resolution:
External Link: SmillaEnlarger
External Link: BenVista PhotoZoom Pro
External Link: Topaz: A.I. Gigapixel
Knowledge Base: How do you adjust the DPI (or PPI) for your renderings?