If you decide to change your vocal characteristics -- especially the "strength" and quality of your voice -- you should do that under the direction of a trained vocal coach (or speech pathologist). The vocal cords are sensitive to "vocal abuse," physical damage from the vigorous, strained, and prolonged use of voice. Perhaps you have experienced that kind of vocal strain in people who have shouted for prolonged periods of time at sporting events and who have found that the strain left them with a hoarse voice.
The cords can recover from most physical damage that results from abuse, but if the abuse persists, the remedies range from inconvenient to unpleasant. From that viewpoint, it is best not to practice vocal exercises unless you are monitored and supervised by an expert.
It is possible, however, to give the impression of a stronger voice without actually changing your voice at all. The trick is to shorten vowels and to articulate consonants precisely. Between vowels and consonants, the vowels have by far the greater power; but in English, the consonants carry the meaning. Therefore, if you say the consonants more clearly and with greater precision, your speech will be heard and understood more easily, and you will give the impression that you have "strengthened" your voice.
That trick is not a substitute for improving your voice, but it will help, especially while you arrange for professional vocal training.