When you want to update to a more recent version of Gnulib, without changing the list of modules or other parameters, a simple call does it:
$ gnulib-tool --add-import
This will create, update or remove files, as needed.
Note: From time to time, changes are made in Gnulib that are not backward compatible. When updating to a more recent Gnulib, you should consult Gnulib's NEWS file to check whether the incompatible changes affect your project.