Help! Version 4 upscales were closer to 2400x1600 pixels. Version 5.2 upscales are about 1300x900 pixels. Is there a way to use the newer version with the larger pixels in the upscale?

Version 5 and up don't actually upscale. They generate at full size. The U button just separates each one out.

The actual pixel count depends on the aspect ratio... but that is a RATIO, meaning 2400:1600 is exactly the same as 3:2 :p

You can now get larger images, though, using the "pan" feature, which adds pixels either to the left or right side, or top or bottom of the image (the little arrows under your result). You can keep panning on the same axis to get ever larger images.

However, if you want larger images with the first result, you need to upscale in a third party program. Any image editor will do this, but to make much larger images without any aliasing, blur or artifacts, you should use an AI upscaler.