How can I modify vertical space between figure and caption?

Modify the lengths \abovecaptionskip and \belowcaptionskip (in the document preamble) to suit your needs:

\setlength{\abovecaptionskip}{15pt plus 3pt minus 2pt} % Chosen fairly arbitrarily

The default values are 10pt and 0pt. (The plus and minus allows the space to stretch and shrink if needed. The numbers specify how much.)

\vspace*{-10mm} placed before \caption command does the trick. Just pick the number that works for you the best.

You can use the caption package for this:

\usepackage[skip=2pt]{caption} % example skip set to 2pt

This will effect all figures.

The documentation says:

The vertical space between the caption and the figure or table contents is controlled by the option skip=amount. The standard LATEX document classes article, report and book preset it to skip=10pt, but other document classes may use a different amount.