I have created a custom list named “K2 Workflow Tutorials” in which K2 workflow will be created to rename folder in document library. Please refer to my previous article to create a K2 workflow in SharePoint 2013 Online.
Go to K2 designer, drag and drop Rename Folder step from the Documents workflow steps in the ribbon interface.
Select a site collection, enter the existing folder name and then click on Next button.
Specify the document library in which you want to rename the folder and then click on Next button.
Specify the new folder name and then click on Finish button.
Deploy the workflow. Create a new list item in “K2 Workflow Tutorials” list with title field value as “TEST”. After few minutes the workflow will be completed and the folder named “TEST” will be renamed with the new folder name in the document library “K2 Workflow Documents”.