Take the SIM Card out of your old phone and put it into the new phone if it fits.
If it's a different sized SIM Card or your old phone didn't use a SIM Card then log into self serve and select phone then change handset and input the # on the SIM Card and submit it. Then take the SIM Card and put it into the new phone and turn the phone on. It can take up to 15 minutes for the new phone to begin to work after activating the new SIM Card.
Not sure if that's the info you were looking for but if it's not then please expand on your question.