I installed Mambo, and now I want to get rid of it, but I cant delete the folder because it created a file in the directory that I cant delete. It is chmod at 644. I have tried to change it to 755, and 777, but any changes aren't saved. Its just reverted back to the original. I cannot rename the file either. Basically, I cant do anything to it. I am using the admin account. What do I need to do?

You should be able to delete a file that has 644 permissions (so long as you are the owner). My guess is that some application is holding that file open, so it can't be removed. You would have to take down the application first, then delete the file. Are you using cPanel > File Manager to change the permissions? If so, remember that you have to check/uncheck the boxes, not  directly enter the new permission numbers. If you're changing permissions through an FTP client, then I don't know what happened.