How do i go about replacing the middle burner on

Remove the cooking grate so you will have unrestricted access, remove the flame tamer (it should be able to come up without effort) to expose the burner. At the back of the grill there is a screw that attaches the back part of the burner to the grill. Remove the screw, then grip the burner and pull it towards the back of the grill, this should release it from the gas valve in the front. To put the new burner in, just do all these steps in reverse...let me know if this works for you, if not I can walk you through it via chat.