As Wigwam says, just phone them up. I did for my Tiguan (lease expires end of Nov this year) – no hassle. They simply ask the current mileage and are fully aware of the lack of suitable cars at the moment.
Good idea to extend for 2 years, as you can upgrade at any time during that time period.
Don’t know how true it was, but when I said I was looking at the new Allspace, the call handler checked and said it was due to come on scheme during the first half of next year. I will wait with breath baited!!