Can't login after my site was moved to a new server

Question

I'm working on a site which is not attached to a domain name yet, so I access to it through an ugly URL like old_server.something.myprovider.co.uk/.../.../

My provider moved me to a new server so I now have to type : new_server.something.myprovider.co.uk/.../.../

Problem is, when trying to access wp-admin, WordPress performs some sort of redirection to the old address and of course it doesn't work anymore. So I can't access the login page.

Is there a way to change the server URL in WordPress without accessing the dashboard ?