The short answer is that there is no easy conversion for a completely general case. LaTeX2.09 style files are very much a mix of formatting and 'additional' code, even more than is the case with LaTeX2e.
More specifically, the LaTeX2.09 style in question has never been converted into a LaTeX2e class. That means that there the change
is not possible: the later does not exist. That leaves you needing to recreate the layout and macros provided by
res_yy in LaTeX2e. This is certainly possible, but I suspect that the effort is not really balanced off by the outcome. The amount of work needed to do the conversion seems at least equal to starting either from
article or a specialist CV class.