Here is an example to rename a file, but you can do it with a folder too.
Select a file. Here we select "Avatar.avi"
Press the MENU button of your remote control, then select "Rename".
Then you can press the OK button of your remote control.
Press OK button again. You can see the numeric keypad appearing and the whole line is already selected (green).
Here you can rename your file with its extension using the numeric keypad.
If you want to use the mouse from the remote control : click here.