Well OK just the neckline. The original was a poloneck, also known as a rollneck or turtleneck. Its was uncomfortable and unflattering, so I performed surgery as follows:
I put the orange sweater inside a green one with the desired neckline. I drew the neckline in with felt tip pen and cut out with sharp scissors.
Then I cut a strip off the old collar and stretched it to fit the new neckline. Sewed it on, serged it and pressed it.
(Excuse the dark mark, its leftover water from the water spray I use when pressing).
This is a much more flattering and wearable neckline for me, so a good rework I think.