cosplayresources:

Earlier this week I had a question come into my dash about lightening a synthetic wig that was ordered a little bit to dark. Unfortunately synthetic fibers don’t work like human hair, and won’t work with most dyes (the one exception being Katie Bair’s Synthetic Wig Dye) 
This tutorial by Rirukuo is an easy guide to Lightening a Synthetic Wig. From every method I’ve seen and tried, this is definitely the most fool-proof, and the easiest.
Here are a couple more methods for ghetto wig lightening

• How to Lighten a Wig (w/ Baby Powder or Talcum Powder) - Video Tutorial
• Accidental Wig Lightening (high-temp wigs only)