They say that the soul is attached to the mortal plane by the means of the body. If the body was to die in whatever way it would, the soul’s connection to this plane of existence would be cut.
Alas, man has always attempted to keep the soul on this plane. They did everything they could; magic, sacrifices, experiments. All of this, just to keep their materialistic belongings under their ownership. All things must come to an end, and no one is exempt from leaving this plane.
There is, however, only one way to keep your soul bound to this mortal plane of existence. If it goes wrong in any way, though, do not say that I did not warn you.
Take your firstborn offspring to any depression in the ground; whether it be your basement or a trench. You must kill them in whatever way you can without injuring their heart or their brain. If for any reason you do this, the slot for a soul to enter the body will be erased completely. Next, you must find a way to preserve the body while you complete the other steps to this. Freezing the body is the best choice, as adding preservatives may lead to abnormal thoughts and actions when your ethereal spirit enters the body. Then, you must find a knife or a short sword. Engrave an eye into the tip; this shows the awareness of the soul entering the new body.
Once you have the sword ready, open the chest of the frozen corpse. This is a physical representation of the entrance into the body for the soul. Now the next part is to have your soul travel into the other cadaver without having your soul enter Purgatory for judgment, in which you almost will be sent to whatever dark, hellish afterlife you may or may not believe in. Also, your soul must be convinced that it has to leave the body, so your own body must die an agonizing death. By this step, many who ventured this far simply quit from all of the emotional stress and creeping insanity, but if you are the single one who will not give up in exchange for eternal life, then you must proceed with this step.
The most painless way to kill yourself to complete this step is dying due to the absence of oxygen. The catch to this is the body may not completely register this as a death, due to the other cellular processes that happen in you. The next magnitude is dying due to the lack of appropriate blood levels. This is assured to make your body register its own death. Once you die... well, I do not know what happens next. God, Zeus, Ra, or whoever you call a deity may catch you while going to your firstborn's corpse. If they catch you, well, have fun burning for eternity.
If they don’t, however, you will enter the body of your firstborn. If they are the opposite gender of you, it may seem very weird at first; but congratulations. You'll wake up to freezing temperatures, a slit in your chest that you may want to attend to, and eternal life. Yup, you now will live forever in your firstborn's body.
Welcome to Hell.