The default screen resolution is 800x600.
You can simply set the window resolution like the following in your Game constructor:
graphics.PreferredBackBufferWidth = 1440;
graphics.PreferredBackBufferHeight = 900;
If you simple want the stuff to appear in full screen mode, do:
graphics.IsFullScreen = true;
If you want to call these codes other than in the constructor, then you need to call:
After the above code.