There may be instances in which you would like to cancel the import of a file that is being imported. This article provides relevant information for that case.
As of now, users are not allowed to cancel a file that is importing. Deleting a file from the File's page will not prevent the file from importing. If you accidentally imported a file, you can wait for the file to finish importing and then delete the data.
Refer to Deleting Data from Beckon for more details on how to delete data.