DPI is only a number. You can change it in your image editor to anything you want. Trust me, the render is exactly the same no matter what DPI you put in Poser. You can take the same image and set different DPI numbers in your image editor, then print, and they all will print differently from the very same image. The DPI number in Poser is a convenience only. You can print directly without going through an editor, but it is totally arbitrary and has no effect on the render itself.