To uninstall Flow, go to Start Menu->Settings->Control Panel->Add/Remove Programs. In there you will see an entry for Flow. Click on it and ask for removal.
<techie> Flow uses MoveFileEx() to have the files deleted on reboot (as an executable cannot delete itself whilst running). This call is not supported on some versions of Windows 95. If the call fails, Flow will ask you to delete the files manually </techie>
To reinstall Flow (say after reinstalling the operating system or changing the location of the Flow files), simply find wherever it is installed eg; c:\program files\ned Productions\Flow and run the Flow executable. This will check the entries within your system registry to see if they are correct, and if not then it will update them to be correct.
Obviously this means that if you have more than one copy of Flow installed, the uninstaller will only know of how to uninstall the most recently executed copy. To avoid this, avoid having multiple copies or simply delete all copies of Flow and reinstall.