When you get it it will be on retention I guess Transfer paid (straight from DVLA)
Take this form V5 / MOT / Tax to local tax office and theres another form I think you have to fill in once there (or log onto the DVLA and check)
Then the DVLA will sort the rest, you get a new V5 sent in post. The tax disc and MOT last time I did it was changed and given me straight away.
Once you have the V5 back tell your insurance, plates on, tax in enjoy.
There maybe something I've forgot, its been over a year now since I have done it (long time for me) although I have another retention reminder the other day.
It use to be done all straight in one go, but that doesn't happen now, its quite quick though.