You will have to take another checkride with an examiner or a DE. I am sure you are aware that it would be wise to go back and get current not only in the plane, but as an instructor. I would recommend reading the FOI again and other instructor materials. It would also be a good idea to do one of the online refresher programs with a company like Jeppeson. I used them at a fairly decent price when I renewed my CFI in January. It would be a good place to start for you. They do a review of most areas you need to know, and also talk alot about some of the new licenses available along with requirements to get them. They also talk alot about teaching methods and strategies for new and old instructors alike. Hope this helps a little!!!

Jason