Just as each person is unique, so is each voice. Every voice reflects the person's character, and trying to change it affects how your view yourself. That being said, there is no denying the preference women have for a man with a deep voice; look at the continued success of Barry White. While nothing short of surgery can take a tenor to Barry’s level of baritone, it is possible to change your voice. All you need is time, patience, perseverance and a little bit of guidance.
Relax. Remove or avoid any source of stress in your life. If stress is unavoidable, learn relaxation exercises and deep breathing techniques. When you’re stressed, your whole body is tense, including your vocal chords. This results in a speaking voice with a higher pitch. Loose, relaxed vocal chords produce deeper reverberations within the chest and a deeper sound in your voice.
Smear a liberal coat of mentholated chest rub across your upper torso before you go to bed each night. This will allow you to breathe easier and keep your throat muscles relaxed, resulting in a deeper timbre to your voice in the morning.
Exercise your voice. Practice humming or singing in the deepest tone your can manage, or try heavy metal scream singing--but not too often. Put on some heavy metal music and sing along, including all the growling and howling, once or twice a week. You’ll notice an itching in the back of your throat at first. This will go away with practice.
Practice speaking more slowly, while holding your head up and projecting your voice from your chest. This will allow your voice to travel further without any extra effort on your part.
Speak from the back of your throat. This can be difficult at first. Try to imagine there is an egg on the back of your tongue when you are speaking, this will help you to keep the throat open and bring the sound from the back of the throat rather than through the nose.