The same way as the humans get. The human or the ghosts are not liberated for the reason they have bundle of Karmas. And these Karmas are manufactured by the tendencies and the desires to get this or that, or to do this or that. When the Karmas are heavy, it gets delayed in getting liberation as the liberation only happens when one shifts oneself from the tendencies to ‘the life of awareness.’

The greatest advantage of human life is to take discretion, with this one can change the course of ones life … he has the options wide open whether to become God or a Devil. On the other hand (leaving some celestial beings who  have some degree of awareness), the ghosts don’t have the discretion so it takes lots of time to get liberation in their realm because their Karmas are huge and they don’t have any steering wheel in their hands. As they keep on living their life slowly-slowly their Karmas start wearing off itself, but this slow path takes a huge time direct correlated with their level of Karmas. And the short-cut route for them comes when the grace of some enlightened human help them to dismantle their Karmic structure that is made of energy.