You can create a Multi-Package Limit by clicking on "Add" in the "Multi-Package Limits" section on your main Online Registration Administration page.

Provide a descriptive name and set the limits that this Multi-Package Limit will enforce on packages. Then click the ADD button at the bottom of the page.  

Your list of Multi-Package Limits will appear just under your list of packages on the main Online Registration administration page. To edit or delete a Multi-Package Limit, click on "Open". Click the "Delete" button to delete it or modify it and click "Save".  

Once your Multi-Package Limit is created, you can then configure your packages to use it.