Why can I modify modules that I installed using Joomla/Mambo?
This is a known issue. The modules install OK, but all the files end up being “owned” by the Web server, not the client login, so you can’t edit them. Luckily, if you download the JoomlaXplorer or MamboXplorer extension, you can edit the files even though they’re owned by the Web server. Be sure to have a look at the accompanying ‘Read Me’ for detailed instructions.