First disconnect the cables that go to the last shelf of the stack.(the red ones in your picture)
Then connect the cables from the new shelf to the ports you just disconnect,
Be carefull to connect a square to a cirkel and NOT a square tot a square.
Then after that reconnect the cables you disconnected in the first step to th newly placed shelf.
Check if the disk are visible (storage show disk -p) and are multipathed.
After you see the disks, if auto assign is active the disks are assigned to your filer.
If not, assign the disks by entering disk assign <disk name> or if you want to assign them all to 1 controller, use disk assign all
After that, you can add the to a new aggregate, or create a new one.
aggr add <aggregate name> <disk> or aggr create <aggregate name> <disk>
Cheers,
Arco