Out of curiosity, why do you want to do that? Note that some apps (poorly written apps) will have problems if you rename them.
That said, what you describe sounds like a permissions problem. Do you have administrative permissions? If not, you won't be able to do it anyway. If you do, and you can't change the permissions through the Get Info window, you could use the Terminal to rename it.
Open the Terminal and type "sudo mv " (without quotes, and remember the space following the "mv"). Drag the app onto the Terminal window and it'll add the path to the app. Now do that a second time, and backspace over the old name in the second path and type a new name. The result should look something like this:
sudo mv /Applications/oldappname.app /Applications/newappname.app
Hit return, enter your password when asked and see what happens.