In Inkscape this is usually fairly easy. As long as the scale is correct, File->Document Properties will easily change the view box dimensions. Your original will have looked like this (this is Inkscape 0.9.4):
and doing a File->Save as and selecting Plain SVG as the Save as type values will update the svg. The exciting times come when the scale is wrong (early Illustrator used 72 DPI, Inkscape to 0.9.1 I think used 90DPI and 0.9.2 and later use 96DPI as px values. If the scale isn’t correct you need to rescale the document (and I think that needs Inkscape 0.9.3 or later, as the scale wasn’t in previous versions I don’t think.) There is a howto here on rescaling using Inkscape:
