Just cancel them in the Mini/Mighty Subscription menu on your TV.
Just contact LIVECHAT and ask for a new mini to be sent out. Note only the first mini/mighty you lease is at a reduced price. The second one is more expensive. Also as its leased you never own them however you can also buy them out right for $170 (Note any free packages in your Optus Fetch Plan won't carry over to a seperaetly bought Mini.)