He also said that the party's 2013 general assembly would be held over six days from Dec 2.
The national-level elections for the Wanita Umno, Umno Youth and Puteri Umno wings would be held on Sept 28, he told reporters after chairing a meeting of the Umno Supreme Council, here.
Najib, who is the prime minister, said party members who wanted to contest posts in the supreme council, divisions and wings could register as candidates on Sept 7 with the state Umno liaison committees.
This is the first time that Umno will be enforcing amended provisions of the party constitution that enables about 150,000 grassroots members to elect the top leadership, and not restricting the elections to about 2,600 assembly delegates as was the practice up to now.
Najib said he hoped that the amended provisions of the party constitution would enable members to elect leaders who could place the party on a stronger foundation.
"We hope that the elected leaders are acceptable to the party and the people... we want leaders who are successful not only in the party but also in the general election as well.
"We hope that Umno can be accepted as the party of choice of the people. It is for this reason that we have to field leaders acceptable to the people and able to reflect a positive image," he said.
Najib also announced that the total number of Umno members as of now was about 3.4 million.
The number included new members totalling 113,959 as of July 22, making up ordinary members (9,043), Wanita Umno members (17,841), Umno Youth members (48,867) and Puteri Umno members (38,208), he said.
