Bulk Renaming of Records
You can rename a document in ERPNext (if it is allowed) by going to Menu > Rename in the document.
Alternatively, if you want to rename a whole bunch of records, just go to:
Setup > Data > Rename Tool
This tool will allow you to rename multiple records at the same time.
To rename multiple records, upload a .csv file with the old name in the first column and the new name in the second column and click on Upload.