Removing a workflow from a list or library does not delete the actual source files used to compile the workflow. Rather, the workflow is no longer attached to the list or library, but the source files remain stored in the Workflows document library of the site. To delete the workflow, see the next section.
- In a Web browser, browse to the site that contains the workflow that you want to delete, and then browse to the specific list or library to which the workflow is attached.
On the list or library menu bar, click Settings, and then click either List Settings or Document Library Settings, whichever is present.
Under Permissions and Management, click Workflow Settings.
- On the Change Workflow Settings page, click Remove a workflow.
Note: You can use the option Add a workflow to make a workflow that
was previously removed available again. But note that a workflow that
was designed in Office SharePoint Designer 2007 is always attached to
exactly one list or library. You can add a workflow only to the list
or library to which it was originally attached.
On the Remove Workflows page, click Remove, and then click OK.
Click OK to confirm that you want to remove the workflow.
Note:- Above Example is for SharePoint 2007 (I provided it for SP 2007 as you didn't mentioned your SharePoint version ) but it works same for all SharePoint Environments.