LTspice IV autozooms whenever there is new data to plot. To zoom up on an area, simply drag a box about the region you wish to see drawn larger.

Note that the size of the zoom box is displayed on the status bar at the bottom so that you can quickly measure differences without setting up attached cursors.
There is toolbar button to return to the autoranged zoom. The undo and redo commands allow you to review the different zooms used.