first things first:
you don't have to uninstall old version before installing the new version, just install new over old.
you do have to make sure the program is *not* still running in the tray when you install the new version.
It sounds like that might be the case for you. Make sure you right click on the screenshot captor icon in your system tray and choose exit.
Then install the new verison and assuming it doesnt complain about not being able to replace a file that is in use, you should be ok.
Let me know.