If you are installing template, module, component and plugins in joomla or mambo the script will take ownership of the file and you will not be able to delete it using ftp.

Here are the three methods on how to delete it:

1. To delete the file is to login to back end and goto Extension Manager->Install/Uninstall and choose the component, module, plugins or templates you want to uninstall.
2. The second method is by using SSH(Secure Shell) to delete the file or folder. Here’s the SSH client for windows “putty” ”. If you are in a shared hosting and your hosting doesn’t have ssh support, download phpshell 2.1. and use the following command to delete the directories, “rm -rf directory”, where “directory” is the name of the folder that you want to delete. For more info on linux command, click here.
3. The third one is by using the joomlaXplorer component. Download it here…. .

You can visit the joomla forum website to find more details/guides about this issue.