Usage is similar in versions 2.3, 2.4 and 2.5. The option is accessed via different tabs.
In versions 2.3 and 2.4, using the /par interface, the option is located under "Users & Groups | UserIDs | Batch Update UserIDs".
In version 2.5, using the /tpam interface, the option is located under "Batch Processing | Update User IDs".
There is more information on that page of the GUI regarding creation and usage of the import file.
A brief example would be a bulk delete file; a text file named 'bulk_test.csv'. The contents would be:
User Name, Update Action
The first line is a header line, with the columns required for this bulk update. In this example, only 'User Name' and 'Update Action' are required.
Once a text file has been created with the above, it may be processed as a Batch Update by clicking 'Select File' and then process file. Note that there is no further option to cancel after selecting 'Process File' - it will be immediately processed.
At this point, the log from the processed actions will appear.