We roll over a futures contract to the next contract during the weekend before the contract's expiration.
After rolling over, and before the market opens, you may see '0.00 (0.00%)' next to the instrument's quote. This indicates that the contract has been rolled-over.
To see the updated previous and coming contract's quote, click on the 'Contracts' tab under 'General'.
Note that before the old contract is actually rolled-over, the volume for the new contract is already much higher. Once the contract expires, its trading volume is zero.