well from my point of view it would actually be quicker to just create a new parametric design in openscad then bugger about with the stl file.

However, what you probably want to try is Meshlab.

Or you could simply load the stl file into a slicer - pretty much any slicer and just resize and then export as new stl file. probably take about 2 minutes.
Umm, so lets actually make that option number 1: load into cura (easiest to use that's free) resize - keep it proportional and it'll reduce the length and diameter automatically, export resized file and you have your resized stl file.