You need to first get the script out of the .rtf file and into a plain text file (open it up in TextEdit and select "Make Plain Text" from the format menu, then save it again as myscript.sh).
Now you can type
sudo sh myscript.sh
The "magic" sh letters there are because as another responder says, sudo will temporarily elevate you to superuser and run a program. In *nix environments, that would be anything with the executable bit set, meaning that someone's explicitly told the operating system that it's safe to run a file. In your case, your myscript.sh has not been "blessed" in this way, so to run it you need to feed it into a program that knows how to understand it. That program is sh, and it does have the executable bit set. Thinking of it as sudo (sh myscript.sh) might make it a bit clearer.
If you plan on running this script a lot, you might want to actually make it executable on its own. This amounts to putting special instructions inside the file that tell the operating system how the file should be run. If you stick #!/bin/sh (this is called a shebang line and tells the OS what to do with your file) on the first line of your script, and then type chmod u+x myscript.sh (this tells the OS that you, and only you, are allowed to execute your file), you'll be able to run the file directly with sudo myscript.sh.