If you want to delete a store/channel which you no longer need make sure to complete below points:
make sure these is no open order for the channel you want to delete. To check for any open order for the channel go to the orders page > click on more filters > select the store name in the channel selector > click on apply. If there are any open orders you will have to archive them. Check this guide to learn how to archive open orders.
Disconnect the channel
Screenshots on how to disconnect and delete a store
Go to channel settings page by clicking on the settings button from the dashboard
Click on disconnect button
Click on delete button which appears after you have disconnected the store
