The Change Number feature in WhatsApp allows you to change the phone number associated with your account on the same phone, and is intended to be used before you verify your new number.
This will transfer your account information including your registered profile, groups and settings from your old phone number to your new phone number; and consequently deletes the account associated with your old phone number making your contacts unable to see your old phone number in their lists of contacts.
If you change your number, your chat history from the old number will continue to be available on your phone with the new phone number, but only if you continue using the same phone.
Ensure that your new phone number can receive SMS, calls and has an active data connection, for you to begin the change process. You should also make sure the old phone number is currently verified in WhatsApp on your phone.
Note that once you change your WhatsApp phone number, your contacts will not individually be informed. Only participants that share group chats with you will notice the change. So, it is advisable that you notify your contacts that your number will be changing to make it easy for them to get to you.
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Insert the new SIM card with the new number into your phone. Open WhatsApp. Go to the WhatsApp Menu Button, select Settings, then select Account, and finally tap on Change number.
Enter your old phone number in the top box, your new phone number in the bottom box. Tap Done at the top of the screen. You will be prompted to verify your new phone number with either an SMS sent to the new number, or a call made to it.
Go to Settings, then select Account. In Account, tap Change Number. You will be asked to enter your current WhatsApp phone number in the first box, and your new phone number in the second box. Tap Done when finished.