Remake STL model from Existing STL

i have a STL model that was done but needs to be recreated so we can have parts of the model editable. We only have the original final STL so it needs to be remade so we can change things on model as it is not editable. We do not have any of the original files to make changes! so we need to make from scratch. Want new file in 3dmax or similar also would prefer someone with 3d printing experience!