can't get into admin panel

When I set up the site before the domain name was pointed to it, the path was “mydomainname.com/~client”. Everything worked fine even after the domain name was pointed but I’ve noticed with the most recent WordPress update that on other sites that were set up this way, the images don’t display any more with my domain name in the path. Usually easy to correct. However on one particular site I’m now getting a 404 error when I try to go into the admin panel. How can I get in there to fix things?