If your account is not an administrator account then the problem could be that you simply don't have permission to remove the application.
And, it might help if you posted what you tried to do and what the error was.
However, assuming you do have permission to delete the app, the problem may be that most applications in OS X are actually folders containing the executable and supporting files. In order to "rm" a folder from Terminal you'll have to use the -R option to recursively delete the folder and all it's enclosed files.
rm -R /path/to/SomeApp.app
Be very careful using the -R option with rm. If you get the path wrong you could end up deleting way more than you expected... and there's not an "undo" option with rm.
Steve