I suggest you read fully Section J of LASORS as the advice given above is only partially correct. It will spell out clearly how long your credits last, what licence or rating you need to get within what time frame and amongst other things the number of sittings and attempts at each paper that you will have. This should be required reading for any wannabee and you should know the pertinent bits off by heart so you are not caught short. On my brush up courses there were always guys sailing close to the wind that hadn't a clue of the administrative side of the game. LASORS can be downloaded off the CAA website and a quick search will reveal all.