I can only speak for myself, but my advice is that you use the old work as an outline and completely write from scratch.
Last year, I returned to an old project of mine, a 3K word short story that I had written a few years before.
Since then, i'd grown as a writter and gotten a few publications under my belt. So, I figured I could get under the hood of this story, give it a tune-up, a few modifications, and turn it into a publishable story.
Boy was a I wrong.
A wierd sorta deevolution happened. It was as if this old story was some sort of kryptonite rendering my new writing powers inert and I fell write back into my old style of writing. Sure, I tweaked it and made the story 'better' but unfortunately, the story had too many flaws to begin with.
And many of those flaws I was unable to see since I was the original architect.
So my take away is that if I am going to revist my older works, then I am best served by just starting completely from scratch. IMO, that is the best path when there is a significant difference in your current skill level vs your previous skill level.
In summary, I think it depends on where you are on your learning curve. I am still growing as a writer and have much to learn, so there is a significant difference between my skill level now vs a year or two ago. However, hopefully, as my skill level plateaus, then there will be little difference between my skill level at one point in time vs another point in time. So, if that difference is minute, then you can probably edit and revise a piece into publishable form. However, if that difference is significant, then you are probably best served by starting from scratch.
Mel...