Let's clear this first! The role of toothpaste in whitening teeth is limited, if any. So first, make sure all the stains and calculus deposited on your teeth (making them look yellower than they originally are) are removed. The only way for this is to get them cleaned by a dentist.
Once this step is complete, the original color will be seen. You can choose to whiten/ bleach the teeth to a brighter shade by using bleaching agents.
Next Steps
Consult a dentist, get cleaning done and then see if you would benefit from bleaching.
Health Tips
Bleaching should be done under supervision. Best results are achieved with in-office bleaching, complemented with home bleaching.