Short version: You can't, sorry.
Long version: ...you can't, sorry.
There's just too many references to the original folder. Windows doesn't change the folder name because it wouldn't be safe to do so, and likewise it isn't safe to do it manually, either. Any program that hardcodes a path to it would be broken by the change.
The closest you can get would be to create a new account and transfer all the files over. But, needless to say, this presents the issue of installed programs, file ownership, and settings.