When you need to stop gutter leaks, you have several options. You can replace your gutter, or repair it. If you choose to repair it, you first need to locate the leak point. You may just need to re-caulk it, in which case you will want to remove the old caulk with a plastic scouring pad. Make sure to fully remove any debris so the new caulk can make a complete seal. Clean the area with denatured alcohol, and let dry before applying a new caulk. You will want to select a waterproof caulk made for metal such as DAP Ultra Clear Flexible All Purpose Waterproof Sealant. Let dry fully, and test.