Two remarks: 1) you should use \centering, and not \begin{center}, as this environment adds some supplementary vertical space wrt the surrounding text ; 2) do you use the subfig or the the subfigure package? The last one is considered more or less obsolete. With the first one, you have the \captionskip length (sees the doc for subfig), which you may change in your preamble.
Use the caption package to customize all kind of captions and refer to its documentation. For quick help on such issues you can take a look at lshort and l2tabu. In this case the documentation of subfig should give you the answer. All packages and their documentations can be found on CTAN.
Supplement the list of parameters for placing your float. The [h] makes no sense, because it's overwritten by the compiler (mostly with [ht]). I suggest to give at least [!ht] for placing the figure. The exclamation mark is explained in every basic LaTeX documentation.