Renewing your rating is not a difficult process. In short, make a minimum of one evaluation jump including the ground training process for either Coach or IAD. Plus a couple other things, like retake the written test and assist in a class. I have listed the complete answer from the 2011 USPA Instructor Rating Manual below.
From page 2 of the 2011 USPA IRM
"F. Challenging the Coach Course or Renewing an Expired Coach Rating 1. For persons with a current non-USPA Coach rating or equivalent or an expired USPA Coach rating a. make at least one satisfactory USPA Coach Rating Course evaluation jump with a USPA Instructor or IE who has served as a USPA Coach Course Evaluator b. assist in at least one complete first-jump course c. attend a USPA rating renewal seminar d. pass the Coach Course written exam with a score of at least 80 percent e. non-USPA Coaches must include a rating card or other proof of the non-USPA Coach rating to USPA Headquarters along with the Coach proficiency card"
From page 108 of the 2011 USPA IRM
"G. Challenging the IAD or Static-Line Instructor Rating Course or Renewing an Expired IAD or Static-Line Instructor Rating 1. Persons with a current non-USPA IAD or Static-Line Instructor rating or expired USPA IAD or Static-Line Instructor rating must— a. satisfactorily conduct at least one complete student evaluation jump with an IAD or Static-Line IE acting as a simulated student using the deployment method for which the candidate was rated, to include all jump preparation, supervision during the jump and debriefing. b. Pass the IAD or Static-Line Instructor Course written exam with a score of at least 80 percent c. Non-USPA IAD or static line instructors must include a rating card or other proof of the non- USPA IAD or static-line instructor rating to USPA Headquarters along with the IAD/static line Instructor Rating proficiency card"