Create a level collection
Use the builtin editor to create your own set of levels. Remember to update collection title, author and description by clicking "File" - "Collection Attributes". Use the same name for the file and title. Example: title "My Cool Levels" and file "My_Cool_Levels.slc". When you are happy with the design, click "File" in the menu and then "Copy to Levels Folder".

Solve all levels
Go to Play mode. Find your collection among the other downloaded ones. Now solve all levels in your set. This is important to make sure that all levels can be solved.

Upload files
Click "Tool" - "Export Solutions" to save the solutions to a file. The file will be saved in the Levels folder with the same name as the levels file. Note that the "Export SOlutions" functio is only available when all levels has been solved. Now start a web browser and go here. Follow the instruction to upload both the level file and the solution file.