Go to Menu > Image Size > VGA. This will keep the size of pictures around thousand pixels so you won't have to fiddle with the size and hamper its clarity.
Drive Safe,
350Z
Why do you want to click the pic in VGA mode.
Capture the pic in the Mega pixel you wish to click.
Then just resize the pic with the help of MS Paint or Picasa.
In MS paint : Go to Resize and select Pixels & type the resolution mentioned below.
I usually keep the Resolution 1632 X 1224.( Which is
2MP)
Or in Picasa select folder and click export with pixel size, automatically the size will be resized.
Which reduces the size of Jpeg but not the clarity.