If you need to delete a round, it generally means that there is some workflow confusion in your setup. An OpenWater limitation is that only the last round can be deleted at a time and you can not swap the order of rounds.
To remove a round, first navigate to your program. Make sure you are viewing your last round.
Under Round Settings drop down menu, click Advanced.
Navigate to the Advanced tab on the following screen and then click Delete Round. If you have submissions forwarded to this round already, you will need to clear their forwarding status back to the previous round.