This year is a leap year when we have 2 months of Adar, Adar Rishon (Adar 1) and Adar Sheni (Adar 2).
The following is the procedure for people who have Yahrzeit in Adar:
If the loss occurred in Adar of a leap year, then the Yahrzeit is observed only once. The Yahrzeit is the date in either Adar on which the person passed. If one lost a relative in a leap year in Adar 1, then the Yahrzeit is in Adar 1, and if the loss occurred in a leap year in Adar 2, then the Yahrzeit is in Adar 2.
If the loss occurred in a non-leap year, there are two observed opinions:
Ashkenazim follow the ruling of the RAMA, Rav Moshe Isserles, that the Yahrzeit is observed in Adar 1. Therefore, you are only a ‘chiyuv’, entitled to an aliya and to lead services, on the Yahrzeit date in Adar 1.
The Mishnah Berurah writes that it is our practice to observe the customs of Yahrzeit in both months of Adar. This includes lighting a candle, reciting kaddish, and fasting (for those who fast on a Yahrzeit), both in Adar 1 and Adar 2.
Sephardim follow the ruling of the “Mechaber,” Rav Yosef Karo, that the Yahrzeit is observed in Adar 2. Within the Mechaber’s opinion, some maintain that the first Yahrzeit, at the conclusion of the 12 month period, is observed in Adar 1. In all subsequent leap years, the Yahrzeit is observed in Adar 2.