Update ASG220 from 7.511 to 8.300?

Hi,

I have a customer currently running 7.511 on an ASG220.

What would be the preferred way of updating this unit?

I was thinking about reimaging the box with the 8.300 iso and then importing the 7.511 backup file?

Is this possible? Or will 8.300 refuse to import older backup files?

Thanks in Advance,

Dominik