Upgrading Reward Flights

If I book a reward economy seat now using 42,500 miles plus taxes of £305.52, and PE reward seats then become available later can I upgrade by phoning Virgin and using the difference in miles (27,500 as the PE reward flight is 70K miles) plus pay any difference in taxes? Or is that not allowed?

Thanks

[mitchja]

Yes, you can do that.

Great, thanks. Now I just need to wait for 1st available reward seats!

Graeme