Hi Andy, gradebookplus isn't a module, it won't work from your modules folder.
To install:
Backup your moodlesite/grade folder.
Put the files from gradebookplus/grade into your moodlesite/grade folder.
Put the lang files in your lang/en folder.
This will load the new code in your gradebook. There are no database changes, so if you don't like the new code, replace the gradebookplus files with your old ones from the backup in step one.
As usual, test the install process and see whether you like the new features, on a non-production site before using this.
To install:
Backup your moodlesite/grade folder.
Put the files from gradebookplus/grade into your moodlesite/grade folder.
Put the lang files in your lang/en folder.
This will load the new code in your gradebook. There are no database changes, so if you don't like the new code, replace the gradebookplus files with your old ones from the backup in step one.
As usual, test the install process and see whether you like the new features, on a non-production site before using this.