A true, physical gender transformation spell isn't possible. Sorry. That's just more than what magick can do for you. But if you are interested in switching genders, for whatever reasons, there are other ways of approaching the issue. Here are two spells that can help you with your gender transformation needs.
Gender Empathy Spell
If you're just looking into switching genders as a way of seeing how "the other half" thinks and feels, this is the spell you should try. It brings out the qualities of the other gender inside of yourself. This spell is the same regardless of your actual gender or orientation.
Wrap the blue ribbon around the pink candle, and then the pink ribbon around the blue candle. Set them up on either side of your altar. Light each one.
Focus your thoughts on the other gender and why you want to experience their viewpoint. Set the chalice filled with water in between the candles. This represents the female element. Gently heat the tip of the knife in the flame of both candles.
Hold the knife between both hands and dip the end of the blade into the water. This is the male. Keep holding the blade in the chalice and repeat the following:
Yang and yin
Which side is in?
Lady or man,
I know that I can.
Groom and bride,
See the other side.
Warlock and witch
Make me switch.
Wave the knife blade through each candle again and set it back down. Drink the water from the chalice. Let the candles both burn out on their own.
You should start to have shifted perceptions within 3 days. The spell will only last a few days once the effects get going. Use that time to really try to understand another gender's point of view.
This is a little different, but can help you gain some insight if you are struggling with your own gender identity. It can give you strength in dealing with it, and clarity when trying to make decisions.
You can make the tea with a small chunk of whole peeled ginger root, steeped for 10 minutes in hot water. Then add a few drops of vanilla extract and a sprinkle of ground allspice. Should taste ok.
Light your candle, then set your teacup on the altar. Drop the bloodstone into the hot tea. Ask the Universe to help you understand your gender and what steps you need to take at this point in your life. Drink the cup of tea, preferably without swallowing the crystal.
I hope these gender spells are helpful, but just remember that it sometimes takes more than magick to get something accomplished.