Appropriate permissions presupposed, you can edit selected properties of categories directly in the media area.
First you must change into browse mode (left column, above the categories).
You will either need the administrator role, or a manager role and permission "Edit categories" for the appropriate category.
Click with the right mouse button on the appropriate category within the result list. In the context menu that appears, select the entry "Preview Image".
In the dialog that appears you can select a new preview image for the category, or you can remove an already existing one.
Click with the right mouse button on the appropriate category within the result list. In the context menu that appears, select the entry "Resort".
In the dialog that appears you can change the order of categories within the parent category. Use the handle next to the respective category to move it to a new position.
Alternatively you can also switch back to an alphabetical order or its recursive variation.
Find & Organize Files
Introduction to Users, Groups and Permissions
User Accounts & Groups
Introduction to Categories & Category Trees
Settings, Texts, Formats
Web User Interface
Web Services & Authentication
Manja user interface
HTML template syntax