You can increase them greatly ... although mine seem to have a top limit, although it may be a memory issue.
When you click OKAY to finish the setup below, it will ask you for a name for the file, so line up your view correctly before you start.
In the 3D go to OPTIONS > SETUP OPTIONS > OUTPUT OPTIONS and check OUTPUT TO FILE. Under there, you can change the image size to whatever you want up to 8192 x 6144 as standard or if you check CUSTOM, you can change it to anything you want. I have output up to 16200 x 7580 which gives a 33 MB jpg - (a 72" wide sign @ 225 d.p.i. - I tried to generate it at 300 d.p.i. but couldn't get it to generate that high) - Although you may be able to generate bigger. I don't know what a practical limit is.