Notice that the new number you want to use should not be already registered as an account on Telegram. And when you change your number, people who had your old number will get this one in their contacts list. Also, all your data will be safe and you will find it in the new account.
Change number on Android
1. Open the telegram app on your Android device
2. Tap the menu ☰ button at the top left
3. tap on ‘Settings‘ at the bottom
4. Tap on your phone number below the profile picture then tap on CHANGE NUMBER and then on ‘OK’
5. Insert your new phone number and tap on the okay icon (tick) at the top right corner
6. Insert the activation code that you will receive as a text message on that number and again tap on the okay icon.