This can be achieved via the Admin Tab - Create/Manage Workflow button.

Note, only Disabled Workflows can be multi-deleted.

To disable a Workflow:

1. Select the checkbox and make sure it is unchecked. If you are changing a workflow from Checked (Enabled) to Unchecked (Disabled) you will need to save the current workflows before deleting them.

2. Next, choose the Delete Multi button on the right-hand side of the screen. (See image below).

A message will display showing a warning about disabled workflows. Click Ok.

3. When the Delete Multiple Workflows window pops up, select all the workflows you wish to delete. You can select multiple workflows with the Shift or Ctrl buttons on your keyboard.