Using the following expression for the Hidden property should give you the desired behavior, as Ashnish Emanuel suggested.
=(Globals!PageNumber <> 1)
When the item is hidden, the objects below will move up. This means that the size of the header should really decrease. This should make the body move up. The size of the body will not actually change; there will be more space on the page for the body.
However, if you set a fixed height for the title, it will not make it shrink, because it will save the empty space after the last element. This will mean that your body will not move up. If you want to create a space between the controls, I suggest you always do this inside the report element (for example: a rectangle, text box, tablix), because this will give you more control over it (expressions).
Another solution is to remove the report header together and work with Tablix with a single column. You can replace TextBoxes in Rectangles cells. The title bar has the same functions as the page title, but you also have the CanGrow and CanShrink property that can solve your problem. You can also define multiple header lines that allow you to hide the entire line with ease.
For a line used as a body, you must then resize the rectangle to the same size as the actual page. And set the Keep Together property to true. This will then be violated in the same way as a regular reporting body.
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