On one of the loops I belong to we ahd a discussion about changing viewpoints of a story from first person to third. A number of us had this experience and found the reason was to make the story better. Mine came with the Mrs. Miller series. The first book was written in first person but when I was revising I found my character had run amok with personal comments on just about everything. I decided to try it in third person and so I did but then I found I didn't want the other characters to come into play. I changed it back again. This time I was able to control the character's asides. They came only when there was something for her to orate about.
So how do you know if you've chosen the right viewpoint. Remember in first person only what the character sees, hears, tastes, smells and touches can be described. Also one must remember your character isn't a mindreader. Having her know what someone is thinking pulls the reader out of the first person and into a sort of foggy place.
Third person allows the writer to explore several people. There is also omniscent where the writer goes into everyone's heads and thoughts. This viewpoint isn't used frequently today. So it's back to third person. How do you revise viewpoint?
Is there a definite point of view? Does the author interfere? If so, change those places.
Is the viewpoint consistent? Watch starting out in one person's head and wandering into another without using a smooth transition. I once read a mss from a new writer where there were three viewpoints in the same sentence. Even when using omniscence that's a stretch.
Are you following the rules? If you drift into the viewpoint of a minor character, this isn't playing right with the reader unless this pattern is established early on.
Is the story strong enough to support multiple points of views? If this is your decisions make sure there are smooth transitions. Don't make your reader suffer from whip lash.
So when revising, consider all these points and choose the point of view that's the best one for the story.