Accidentally modified WordPress URL and can’t access wp-admin

I was trying to solve the permalink issue / 404, I was reading this thread here and read Jawntech’s suggestion on tinkering with the WordPress URL:

In the field “WordPress address (URL)”, change the url to either have the “www” or not. Click “Save Changes” on the bottom of the page. Then change it back. Repeat, at least to get it to whichever you’ll want your blog.

I did that, I changed maberui.webs.upv.es to http://www.maberui.webs.upv.es, clicked SAVE and voilà, can’t access my blog wp-admin anymore. Have I fed up my blog or is there any way I can revert it?

THANK YOU, I’m kinda desperate,

Elena