How do you change Google Desktop to work with a different user?

The previous owner of my computer installed Google Desktop under his user name. I now have the computer and I use it with a different username. I am an administrator on my computer. But Google Desktop won't work with my user name, because it says it'll only work for the user who installed it. Likewise, I can't even uninstall/reinstall, because it wasn't my username who installed it. And the original username has been removed from my computer! Help! What do I do??