H2 spacing problem

I appreciate any help I can get solving this little problem.

If I have a headline (using h2 markup) that runs onto more than a single line, the lines are spaced too closely and step on each other.

I know I need to simply change an attribute of h2 in the stylesheet, but I don’t know which instance to change or exactly what I need to add (increase the margin? padding?).

Instructions gratefully welcomed!

Elizabeth