I cant install or un-install itunes!

Hello,
I cant install the latest version of itunes everytime I try a message pops up and it says something about an error and that nothing has been modified. I thought maybe I should un-install my older version of itunes and try to re-install it but I cant even do that. It says it cant find the location or some file and now I cant even access my itunes. I dont know what to do. Help?