If replacing your current flush handle with a different style, make sure that you take note of where the handle is located on your tank; some handles are made specifically for front or side mount applications.
Once you have removed your lid, disconnect the flapper chain from the handle flush lever. Remove the mounting nut located on the inside of the tank that is holding the handle in place.
Remove the handle and flush lever by pulling it through the mounting hole. Remove the nut and washer from the new handle. Insert the flush lever arm through the mounting hole and slide the washer and nut up the arm.
Secure the nut ensuring a tight fit but do not overtighten to avoid cracking the tank. Reconnect the flapper chain to the flush lever and flush the toilet to check for proper function. Adjust where the flapper chain connects to the flush lever accordingly.