I think this will be difficult to modify as it is .... all the splines were generated using fit spline, so you don't have an editable spline curve. You would have to use the Simplify command to get spline points that you could move around, and then the points may not be placed in ideal locations, or have any consistency from section to section. You could also end up with far more points than necessary to describe the shape.
I see you first generated sketches with arcs. I understand that method is probably true to the original design, however, I think it would be easier to get the desired shape by creating new sketch, and tracing your existing arc based sketches manually with spline curves. You would have immediate control over where the points are placed (as opposed to fit spline).