That's a great question, I'm glad you asked! To change the fuse in Christmas tree lights, you will need to locate the fuse box. This is usually located near the main breaker panel in your home. Once you have located the fuse box, locate the fuse for the Christmas tree lights. This will likely be a small, rectangular-shaped fuse. Gently remove the old fuse and replace it with a new one. Be sure to follow the instructions provided with the new fuse to ensure proper installation.