To delete a channel, just click on Delete in the general tab of the channel detail screen.
This action is not available if the channel is currently deployed (You will find the Delete button is grey and can't be clicked on ). If it is the case and you want to delete it, you must first undeploy it from the production systems and this can be done by clicking on Disable from the General channel window then deploy the environment .
A confirmation screen will be shown.
By default, only the channel will be deleted, not the elements (gateways, message definitions, transformations, ...) that the channel could reference. But it is possible to also delete the elements, thanks to the More options button in the confirmation screen. Just click on the elements that you also want to delete. Note also that this list only includes elements that are deletable, i.e. elements that are not referenced by other channels or transformations.