If you want to change the names of all of your replicates, you should create a Custom Report that includes the "Replicate Name" column.
The values in the Replicate Name column can be edited in the Document Grid so you can easily paste in a list of new names.
You can learn more about custom reports and the Document Grid here:
https://skyline.ms/wiki/home/software/Skyline/page.view?name=tutorial_custom_reports
Also, if you want the replicates to be named by applying some sort of rule (e.g. adding a prefix or suffix or even something more complicated) to the names of the files, you might be able to achieve what you want by doing something on the "Result Files" tab at "Settings > Document Settings".
You can read about Result File Rules here:
https://skyline.ms/wiki/home/software/Skyline/page.view?name=ResultFileRules
It looks like page 51 of the Grouped Studies tutorial was talking about defining replicate annotations which would let you provide additional information about your replicates. That is a useful feature, but if you want to rename your replicates you should create a custom report that includes the Replicate Name column.
-- Nick