You can't be anything else but human for now in this live and in this world.
But a spirit guide will most likely teach or guide you to something or somewhere be it in Astral Projection, meditation, helping you find out information and new methods of magick working and belief system mechanics. They can also show you things such as your spirit animal, power animal, etc and sll sorts of things
The general term of spirit can be human or non-human beings of energy that can manifest into things easier to percieve, or understand. They can be from any level or realm, they can be mean or nice. Incorporeal beings in a nutshell, really. They don't always help you, they're just there. But you can get to know them too, but it doesn't mean that they will teach you anything, and you might need to give them something in return for a favor.
I find spirit guides and spirits are the same thing, at least in my practice. My spirit guides, however, are aimed at protecting you from whatever may harm you, and tend to help you through the rough patches in your life. They may also come and go throughout your life. Some will stick around to teach and when that lesson is learned, they'll pass the torch to someone else. Spirit guides can also be family members.