You can only rename unlocked files. Click on the rename link on the file you wish to rename. The screen will change to a screen with an input box. Type in the new filename in the input box (be sure to write the extension. The extension is information used by the operating system on how to open the file). Press continue if you wish to rename the file. If you do not want to change the filename, press Cancel.
Invalid characters will be replaced by the character '_'.