They have the same rights. They may maintain membership or leave as they see fit. Again, read the Declaration of Independence and try to grasp the concept put forth.
DL, DD is partly correct, some states have rights and other states do not. In the War of Northern Aggression, the rights of the Southern State were less than the rights of the northern States, particularly relating to economics.
The North saw the South being able to conduct business with other countries as against the rights of the North to remain the sole supplier of industrial goods to the South.
So a state has the right to walk out of the union and leave behind any responsiblility for obligations like debt which they helped accumulate, take every bit of national property that they can get their hands on, and the other states have the right to sit back and suffer the consequences without any recourse? That doesn't sound like an equal partnership to me.