The error message you quote tells you exactly where the file you need to edit (which, once again, is not the hosts file) is located:
/Users/[local client username]/.ssh/known_hosts
…and it also tells you which line contains the (old and thus incorrect) host key, which is line 4. Edit that file with whatever text editor you like (nano works fine: nano ~/.ssh/known_hosts; ~ is a shortcut for the user’s home directory) and remove that line–in addition to knowing that it’s line 4, you can also identify it by the fact that it will begin with the host IP address (192.168.50.63). Then save the file (Ctrl-X will exit nano, prompting to save) and try connecting via SSH again.