Torx head screws come in all sorts of different shapes and sizes, but the head of the screw always has the familiar star pattern. Torx head sizes are designated in numbers, such as T20 and T40, with the larger sizes designating larger sizes of stars. A Torx 4 is also known as a T4 screw, which requires a T4 Torx-head screwdriver to remove. The Torx-head screwdriver has a free-spinning top that allows you to push it in place while turning it. Torx 4 screws are fairly small and are most commonly found in small electronics and cell phones.
Place the end of the T4 screwdriver into the star-shaped insert on the top of the screw you want to remove. Make sure it's seated properly by giving it a quick twist. If there is any slack at all, consider using a larger torx-head driver.
Hold the middle of the driver using your thumb, index and middle finger and twist it counterclockwise. If you can't loosen the screw, push the screwdriver toward the screw using your palm, and allow the end of the driver to spin in your hand.
Turn the screw until it's out of the nut (or other object it's screwed into) using the driver. If necessary, you can also use your hand once the screw is barely tightened in the object.