Don't quote me, but I think he can do it 2 ways.

1) Buy a rook membership, then when that expires, you will be turned into a "knight" for however long you have left on your current membership.

2) See if you can "convert" your knight membership into rook membership - that is let say for every 2 months of Knight = 1 month of rook.

Again, best thing to do is wait for Fencer, or send him a note in case he does not see your post in here.