How do I move a design to another folder?

From inside the design

Click the folder icon in the top navigation bar, next to the design name. Select the folder you want to move it to.

From in your Library

1. Select the design you want to move.
2. Click Folder in the action menu on the right.
3. Click Move to.
4. Select the destination folder.

You can also select Duplicate file to keep the design in its current location and add it to another folder as well. See Can I make a copy of my design? for more on duplicating.