Can't access wp-admin

Is there way to access, and change details of wp-admin offine?

I have the site hosted at http://www.myhost.com/mywebspace/thissite

I had http://www.mydomain.com forwarding to the above address.

I got the host to set up a vhost for me, and in general settings on my dashboard I put http://www.mydomain.com in WordPress address (URL) and Site address (URL).

But something has gone wrong, I cannot get into http://www.mydomain.com/wp-admin nor http://www.myhost.com/mywebspace/thissite/wp-admim

Is there anyway to change the details of WordPress address (URL) and Site address (URL) back to the original setting another way?