Summarize this article:

Take the hoodie that fits too snugly around your neck and lay it flat so the neckline isn't bunched up at all. Try to work on a table or counter instead of a bed so you don't accidentally cut into your bedspread. Pull the front of the hoodie in opposite directions so you can easily see where the 2 sides of the neckline meet. The 2 fabric layers will meet in a V-shaped point. Use a sharp pair of scissors to cut a slit in between the 2 layers of fabric. Make the slit go in the same direction as the upper layer of fabric so the cut isn't noticeable. Pull the hoodie on and decide if the neckline is comfortable. If it's still too tight, extend the slit you cut by another 1⁄2 inch (1.3 cm) and try the hoodie on again. For a rugged look, use your hands to tear the slit more instead of cutting it.

Summary:
Lay the hoodie on a flat surface. Use your fingers to spread apart the neckline where the 2 layers meet. Cut a diagonal 1 inch (2.5 cm) slit where the edges meet. Try on the hoodie to see if the neckline is as loose as you'd like.