You can either center the picture, or have it on the left with no text beside it.
Take a look at this picture from the support documents:
http://en.support.files.wordpress.com/2009/08/image-settings1.png
Pay attention to the red number 5 where you choose how to align an image: the options are left, right, center, or none.
A picture aligned in the center will appear in the center of your post area above text which follows.
A picture aligned with "none" will be on the left with text below it, blank space to the right.
/OPINION_HERE:
Looking at your post, it might look nice if you chose the alignleft option. Your text is longer than the picture, but if you were to go into the advanced settings you could adjust the vertical space on the line that says image properties. Put a number, say perhaps "15" in the box. Update.
/END_OPINION
Here is the complete support article where that picture appears:
http://en.support.wordpress.com/images/