To edit pre-made experiments or to author your own you would use the LabAuthor software, part of the LabTutor Teaching Suite.
First, install LabAuthor on a different machine than the LabTutor Server as it will cause issues with the Server if installed on the same machine. That machine could be your office computer or any computer which the students do not access. You may download the current version of LabAuthor HERE. The license code for LabAuthor is located on the back of the LabTutor Teaching Suite DVD installer disk case you received when purchasing your system.
Also, the LabTutor 4.5 Suite Admin Guide (download HERE) and LabTutor Best Practices Guide (download HERE) are handy references to keep on hand when working with LabAuthor and LabTutor. Please refer to pages 48 - 59 of the LabTutor Best Practices Guide for LabAuthor best practices. The steps for installing LabAuthor can be found on pages 34 - 35 of the LabTutor 4.5 Suite Admin Guide.
For more information on how to create and edit experiments with LabAuthor, please review the LabAuthor Basics: Editing an existing LabTutor exercise video located HERE.
Here are a few more helpful videos which discuss how to use LabAuthor and LabTutor.