You can do as another-view says or:-
If you want to forward the e-mail, click Forward and the complete e-mail will appear in a new window. Highlight all the existing e-mail address by left clicking your mouse and dragging across and down all addresses, then click delete. Some times you can't delete all address at once, you may have to do it in stages. When you've deleted all existing addresses. Type your message at the top of the message window. Enter the recipient's e-mail address and send as normal.
If you just click on Forward and type in the address you want it to go to then that person will also receive the addresses of everyone listed in the e-mail You MUST delete them before forwarding.