To renew or extend a number, just tap on top title bar of the app to show the list of numbers you have.
Next, tap the gear icon next to the number in the dropdown box and you will see Extend/Renew number.
Tap on that and you have the option to renew the number for 1 month, 3 month, 9 months or 12 months. Please note that if any number in your account expired, the text and minutes balance will expire and so as long as you keep any number active, they will not expire.
