Hi peter. It shouldn't be to much of a task to shave a bit off the neck.
If you don't want to remove to much thickness but more so want to adjust the profile and soften the shoulders, just hit it with some sand paper (180g, 220g).

If you want to take a little more off, you will probably need a file. I would use something like a 2nd cut file or something on the smooth side. I could be easy to over do it with a rasp file or similar. Plus using a 2nd cut file will leave you with less sanding to do and won't take to much effort to remove what you need to.

The main Area's to watch are around the heel and headstock. You want to avoid touching the flat sections so the transitions keep a sharp line.
When sanding and filing the back of the neck you want to work the full length of the neck and equally on both sides to keep it uniform and avoid any low spots.

It's just sandpaper and wood, what can go wrong.