4000 x 3000 is the max resolution. If the images are not as sharp as you expect, you can turn up the sharpness in the camera settings. They also sharpen up nicely with Photoshop or other computer software.
The best thing to do is crop after the fact. If you change the camera to 16:9 you'll get the same 4000 width with fewer horizontal pixels. In other words, that mode is a crop. If you crop it yourself in post, you'll be able to pick the best crop location and likely get better resulting photos.