Edit .bash_profile of the user:
# User specific environment and startup programs
#PATH=$PATH:$HOME/bin <--- comment out the existing
PATH=$PATH:$HOME/bin:/path/to/metasploit <--- path to the directory where the program is
Now logout and log back in.
Edit: I guess MS3FGX's suggestion is better if you want all existing users and future users to have instant access to the program without having to modify their bash_profile individually.