there are two little magnifying glasses at the bottom right of the screen. you can use them to zoom in and out without actually changing the size of the render ouput. That way if your render doesn't fit on screen you can zoom out and still select and (re)render that little part that used to be 'outside the screen'. You use the one with the + on it to zoom in and the one with the - on it to zoom out. (obviously)

(_/)
(='.'=)
(")(")This is Bunny. Copy and paste bunny into your signature to help him gain world domination.