I have made some changes on my workflow i want to rollback to old one how can i do? I search it but in 2013 designer under All files -workflows i can't see the workflow.
A Sharepoint designer workflow? To re-activate an old one, go to the list, settings, workflow settings, you should see the different versions. Click (strangely enough) Remove a workflow...re-active the old version.
Or, for the source files from sharepoint designer navigate to workflows, find yours, expand it until you find the .aspx and .xml files. Right-click and choose version history.
Visual studio doesn't do versioning.
Refer also this