This is called Pattern Grading. If you can get a hold of a copy of Fit for Real People by Palmer Pletsch, there is a clear explanation of the basic principle and some nice diagrams. This won't be a step-by-step tutorial, but would give you an idea what you'd be getting into.

If you are a detail person and don't mind time-consuming precise work, you may just succeed, but it's not something to attempt if you are short of time or inclined to be approximate with measurements!

Also remember that women were a different shape in the 1950s (think corsets!) and you might find you need alterations for fit as well as size.

Good Luck!
AJ

Here is a link that might be useful: Book

In addition, you might have to round the darts out since bras are different now as well as pattern sizing.