You must realize that you are a Spirit or like Kreiter says a Ghost, and on top of that you are non-local which means you are already everywhere and in everything. This physical world we are living in is an energy-illusion-place stuck in your mind. Your physical body is an energy-illusion-thing stuck in your mind. It's the opposite of what a lot of people believe about supposedly being stuck inside the matrix or being stuck inside their bodies. You are not stuck in anything, everything is stuck inside of you including all and every dimensions.
The matter entirely becomes then to stop focussing on this world and on the physical body, to forget them as much as possible and instead to focus on the astral body you want to have and the place you want to be in. The more you forget about this place and focus on some other place the more you will be there.
I think the go-to book for discovering that you are a spirit is William Walker Atkinsons "Arcane Formulas", and how to move around this >>/9494/ . Even Kreiters earlier book, "out of body experiences quickly and naturally" would be enough imo. The rest is entirely your practice and realization and how much energy you can put into astral travel. I wouldn't know any other way to go to other dimensions and I think this is the proper and real way to do it.