How Can I Make /bin/sh point to /bin/bash?
As shown on this Ubuntu wiki page, you should run
sudo dpkg-reconfigure dash
and select the option not to use /bin/dash as the default shell. Making the change this way will not only fix the symlink /bin/sh, but will also configure other parts of your system to behave correctly, such as making sure that man sh points to the bash manpage instead of the dash one.