Cant access admin page cause I changed my URL

Unfortunately I experimentet with changing the URL to my blog
inside the admin General page. I changed the URL in both fields
(there are 2 fields – dont recall their names) and now I cant
access my admin page through that new URL. I just wish to go back
inside the admin page, and re-do the change back to the original
URL – but shit – how do I do it, when I wrote af wrong URL ind the
2 fields – please please please help