Actually you need to go to the aaRedeemMiles and follow the instructions.

-Your Diners Club account information is required to process the transaction.
-Redemptions must be made in 10,000-mile increments.
-The maximum number of AAdvantage miles that may be redeemed for Club Rewards points is 50,000 miles in one calendar year.
-Club Rewards points will be automatically deposited into your Club Rewards account in 3 weeks.