The option to delete a workflow is available if you have the correct role and if that specific workflow has been flagged as delete-able. To delete it:
1. Open the workflow you want to delete
2. Click the three dots on the right of the workflow
3. Click the option 'Delete workflow'
The page will refresh and the worlflow and it's form(s) will be removed.
Please note that this process is not reversible, so proceed with caution.