Fixing a novel is like remodeling a house. It takes time, energy, and experience. Sometimes it even takes money to fix a book, by hiring an editor.
As you look at a house/your novel, is it on a solid foundation/plot? How’s that location and setting? With the changes you make, will people like it? Will you like it? Is it functional or all a cluster mess?
What parts do you want to change? Most houses and novels could use improvement. Even if it’s just a little attractive paint. Or an entire remodel.
The two biggest selling points of a house design are kitchen and bathroom. What about a novel? You need an interesting plot and intriguing main character. How can we make those better?
Can you sell this thing when you are done polishing it? Do you even want to sell it or just keep it forever?
Finally, will it look good enough after its finished to be worth your efforts?