You can replace the binaries with the binaries you get from their installer. You can download their 64 bit installer, install, and move the binaries it installs into the normal SmarterMail Clam64 path. Make sure you kill Clamd.exe before you do this.
You shouldn't even need to restart SmarterMail. Once the binaries are replaced, disabling and re-enabling Clam will boot it back up.