Hi Vamsi,
There are two checkboxes on the screen ( txn /SAPSLL/LLNS_UPL101) used for uploading of the text files under the section Overwrite texts of the following objects
1. Change texts of Numbering schemes
2. Change texts of Structure Level.
Please select both of them and try, it should overwrite the files. If I were you, I would try with only the first chapter texts.
Thanks,
Shrini