There's no option to move the labels, but they're usually at the top of the bar (or middle for stacked bars), so I may be missing something if yours are at the bottom.
A couple ugly work-arounds.
- Use text annotation (in the Tools menu) and enter the text manually
- Put the label in a label column and add labeled markers to the graph under the top of the bar. The labels for markers ("Points" in Graph Builder) are movable.