Problem with upgrading – where are wp – directories?

I have a question so basic that I cannot find documentation for it anywhere and I am hoping someone can turn on the light for me:

I had my wordpress site built for me by someone I no longer can contact. I am running version 2.51 and have decided to upgrade.

Backup worked fine. Now. What I have no idea about is how to locate and delete the old wp-includes and wp-admins. Documentation always says “the files and directories where you installed wordpress” but as I did not install it I have no idea where wp-includes,wp-admins and wp-content are, what they are etc. because I never had wordpress installed on my computer. Are they on my server? How do I get there?

Any hints are greatly appreciated.