How do I wind my McCulloch weed eater

The inner spool that sticks out about an inch will unscrew. You must hold the outer housing while doing this. Some weed eaters have a small hole just above the housing. You can stick a nail into the hole and it will lock the shaft from turning. Once the spool comes out you can put in a new spool or coil just replacement string. Take a scap of the old string with you to the store because the stuff comes in about 10 sizes.