Actually, there's only one uninstaller (for each hack), the >= 3.2.1 thing is specific to the jb *install* only

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AFAIR, if you actually *get* to see the 'jailbreak already installed' message from an installer, it probably means you have the *other* jailbreak installed.
You probably should be able to reinstall the *same* jailbreak on top of itself, and if it's mine, you could also just manually put the 'linkjail' folder from the install package on the root of your Kindle. (You'll probably need to restart your Kindle to be able to install/uninstall custom stuff after that).