Changing Directories

I’m far from a computer wiz and I need help changing directories. What files do I need to change and where the are located. A friend uplaoded it and the way he set it up makes for a long URL. If someone has the time, I’d appreciate the help.

Here is a sample of how the URL is now:
http://www.mydomain.com/wordpress-1.5-something/wordpress

This is what I want it to be:
http://www.mydomain.com/blogname

So basically, just move it up a directory and change the name from wordpress to the blog’s name.

Thank you in advance.