The position of the labels that are part of the graph plot can't be modified. It's possible to create independent text labels and move these to the positions of the graph's nodes. Here's a post describing how that would work:
You can then manipulate the positions either by assigning to the properties of that text object's handle, or by moving the labels by hand.
For the edges, the same is possible, you would probably want to compute the mid-point between the source and target node's coordinates in that case.
