Accept your limitations before going to a lot of trouble trying to learn to belt. Belting requires thick, short vocal chords and if you don't have them, it may be futile endeavor. You may have to make do with a less than hearty belt.
Hire a singing teacher to work with you to get the most out of your voice. The instructor will put you onto singing scales, something you may not do on your own.
Practice hitting very deep and loud notes. Bring the wind from deep in your chest as you make the sound. Hold your hand over your abdomen to make sure your diaphragm is moving. Take deep breaths and operate your abs as if they were and accordion.
Work out with weights to strengthen your back and your abs so that you will be able to control them better. Add neck exercises too because you need to hold your head still as you let the air flow out.