Open the Rename item form by either of two following ways:
The first way
Select your desired file in the Workspace panel.
Go to → from the top menu.
The second way
Right-click your desired file in the Workspace panel, then click Rename from the drop-down menu.
Enter the new name into the Rename item to field in the Rename item form.
Click Rename to take effect.
If your new file name has been existing in the target folder, you will receive an error message.
Do not forget to undeploy the REST Services if they were deployed before renaming.