Use the inspector
To alter the space between paragraphs - click on the paragraph you want. Then open the inspector and choose the text tab (i.e. with the T on it!!) and under the spacing section there is a slider for space after the paragraph. Adjust this as you see fit.
If you want to, at this point open the style drawer and click on the little arrow to the right of the Body text style and then you can either update the definition to alter all the body text this way or better create a new one.
Hope this helps
Kev