Can I delete a customer/vendor?

Yes, you can.

In the Customers or Vendors page, select the customer/vendor you wish to delete. In the details page, click on More on the top right corner and select Delete from the drop-down.

Note: You will not be able to delete a customer/vendor if transactions have been created for it. The transactions for the particular customer/vendor have to be deleted first after which you can proceed to delete the customer/vendor.