I wrote the series I am currently publishing about ten years ago. When I look back on it now what I had there was a shell. I was very much like you, I loved the story, the characters, but the work needed a lot of, well, work.
What I did was as follows. I read a chapter, now my chapters are long and I break up sections with *** I took all the text down to my first break and copied it onto another word document, I read it, understood what I wanted to say and the importance of that section. Then hit enter a few times at the top of the document, and using the text below as a guide, rewrote it. Once it was done, I pasted it over the original, saving it under a different name for the first edit, then did the same again for the next section. Some parts stayed similar, others got a complete rewrite and were nothing like what I had originally written, then there were also new additions and ideas I hadn't included before. Then there were a number of easier full edits once that was done, but the result was, I ended up with what I hope is a good book, from what I now look on as a draft copy.