Before you read any further you much first understand one HUGE misconception. That misconception is the belief that you cannot lower your voice and that you are forever stuck with the one you currently have. Not every radio DJ or voiceover specialist was born with a low voice. It took vocal training and practice.
Step 1: Be Patient and Stick With These Excercises
You can't get a masculine voice overnight but that doesn't mean you can't get one fairly quickly. Within a few weeks you can have a deeper and more commanding voice just by practicing some vocal exercises. That being said, you must treat these exercises as if you were working out your muscles at a gym. If your goal was to get bigger you wouldn't just go to the gym whenever you felt like it and you sure as hell wouldn't slack off while you were there.
The same can be said about lowering your voice. You can't expect to get a lower voice if you don't give it the time that it needs.
Step 2: The Exercises
There are lots of different exercises that you can perform to help get a lower voice. One exercise is to sing DoTiLaSoFaMiReDo in a descending manner. If you do not have a singing background you can youtube scales going downward and learn how to sing this properly.
After singing that first set start by singing the next "DO" one note lower. Then repeat the whole set. The idea is to get progressively lower until you can't anymore. This exercise and some others are better described on 100voice.com but you should get the general idea.
Repeat this exercise (along with others) 2 times daily until you cannot get lower with your voice. Make sure not to overdo it.
Step 3: Watch This Video
Watch this video and check out the full guide that he talked about. Click here to visit the DVM guide that he mentions. Consider getting the guide if you really want a low voice. It looks a little weird and some of the techniques are strange but it works. If you want to get a deeper voice this is the best way to do so.