You can convert items (categories, projects, tasks) into each other.
This is especially helpful when you imported your data from another app and need to adjust the items to fit Marvin's data model.
How to convert an item
To convert an item, click on it's edit icon on the right and then click the icon for the item you want to convert to at the top.
Turn a task into a project
Turn a project into a category
Turn a category into a project