Do you work on an OS X Mac by any chance? If so, you cannot see the .htaccess folder on your system. If you have Fetch or another FTP program, you may find it sitting on your server space, however.
If so, rename it on the server (I just put an x in front of the leading period), then download it.
Add your new statements to it, and upload it, letting it overwrite the older one. Then delete the leading x.
If you do not work on a Mac (or some other ‘nix system), pardon me for butting in! <g>
EDIT: Oops, I see you did not see it on your server. If it exists, it will be on your domain’s root.
EDIT 2: There is an .htaccess tutorial on the Apache.org web site:
https://httpd.apache.org/docs/2.0/howto/htaccess.html
Kathleen