You should be able to do it in AWM as long as you have a recent enough version (220.127.116.11?).
- Select the cube in the navigation
- Modify the name field
- Press Apply
You can also do it using PL/SQL (as long as the AW is not attached by any other session.) Just replace "OLD_CUBE_NAME" and "NEW_CUBE_NAME" as appropriate. This assumes you are running as the owner of the cube.
'<Metadata Version = "1.2">
<Cube Name = "OLD_CUBE_NAME" NewName = "NEW_CUBE_NAME" ETViewName = ""/>