Changing and updating collars is always a bit of an extensive project, but I never regret it. It completely changes a piece.
This is the original shirt I used. See that amazing and pointy 70's collar? It had to go.
I unstitched the collar from the neckline. Then, I removed the collar and flipped it inside out. Once it was inside out, I mapped out and measured the width I wanted the collar to be. Then I sewed the new Peter Pan collar shape. I flipped it right side out, carefully pinned it back into the neckline, and stitched it back into place. Lastly, I stitched about 1/4 inch around the perimeter of the collar to give it the finished look.
Then, I changed the sleeves using this method.
Heres how it turned out:
Close-up side by side
Side by side