The reason why the third estate was so unhappy was because they had 95% of the people which were peasants and they were treated poorly and overlooked by the two other estates. This system was unfair because of the distribution of power, wealth and freedom. The third estate was completely excluded from any political action.
To make the third estate equal, then they should be able to vote with the equal amount that they have that votes. So they should change the voting system to make it an equal voting process and so that the results are equal.
The third estate wanted to be equal with voting and everything that the second and first estates were doing. The third estate started the french revolution to be equal with the other estates and to change the voting system.