First locate the ear tabs inside the wig cap.
Make sure you're cutting the side that bearing the ear tab.
First make Cut #1 on both sides, one on the right ear tab as shown. And do the same on the left ear tab.
After making Cut #1 on both sides of your wig, put it on your head to see how it fits. If you need more room, you can go ahead and make that Cut #2 on both sides of your wig.