To cancel an order you need to navigate to the Orders page and click on the order you want to cancel.
On the top of the screen, you can see the More Actions button, clicking on it you’ll see the list, at the bottom you’ll see the cancel order button.

Here you can see the following options

• Send an E-mail to notify the customer
• Restock Items
• Cancel Reason

After clicking on Confirm, the order will be cancelled and if the order is from a connected sales channel that status will be changed in the channel as well.