how did the tang dynasty change china?

Actually, it is more suitable to say that Tang made a great effect on China, instead of changing China.
As one of the most glorious dynasty in the ancient China, it initiated the organizational structure 'Dao' and 'Fu' to divide the political districts. Besides, it had the the central official system and local official system.
The national talent selection system helped the Tang Dynasty assisted by a large number of talents, the literal and the warriors.
In addition, during that time, the emperor had started the international diplomacy, such as to obtaining the Buddhist scripture and to send the students out to learn the foreign technology then.