Looking to move as well, you can either go down in person (temporary ticket office) or over the phone. I am sending the lad down with a list of preferences of where we want to move to.
At the present it will be any seats not renewed or not allocated to a season ticket, this will probably change throughout the 3 days as people move.
Like you haven't moved before so not sure how smoothly it will go, where are you looking to move to?