if you log into your account on line you should be able to find this.
If not, call 789 on your mobile and select the "I'm thinking of leaving option". You'll then be given your upgrade date which is when your contract ends and you can apply for an upgrade within 30 days of this date.
If you want to say thanks > click 'Kudos'. Answered your question? > click 'Mark as Helpful Answer' also.