This is the normal procedure for a BT ADSL2+ upgrade. First the exchange is upgraded, then your line is enabled for ADSL2+ but you remain on an ADSL Max. Finally, you can upgrade your service to ADSL2+ if you wish. That's the stage you've reached. I imagine that they call it a regrade rather than an upgrade because it's just a shift to a different service; in most cases it will give you an improvement in speed, but not in all cases. If your current connection speed is in the region of 5 Mbps or less, you may not see any improvement.