You can change the folder name by clicking on it, and then typing new name. You can't delete root folder though you can change its name. You can clear all message in folder by selecting from 'File' menu 'Clear folder' or by clicking mouse right button and selecting 'Clear folder'. To Add a folder first you'll have to select it parent folder and then from 'Options' menu selecting 'Add folder' and typing the name of folder in the box which appears and click 'OK'. To Delete a folder select the filter you want to delete, then from 'Options' menu take 'Remove folder' and answer 'Yes' to the promt.
Bug reports are welcome.