Hi Susan.
I will share two items regarding your situation. First, the modifications to your htaccess file involve a replacement language called Regex. The code you are copying and pasting are regex expressions. Basically they say "when a URL meets this condition, rewrite the URL as follows....". In your case, the original regex expression was not correctly written (a common occurrence) so you did not receive the desired effect.
The changes need to be made in your .htaccess file. The htaccess file controls all access to your website. A single character out of place can mean your entire site is unavailable, URLs are improperly redirected, or security holes are open on your site. On the one hand, you can copy and paste code into your htaccess file and it may work. On the other hand damage can be done. It also makes a difference where you locate the code within the file. Varying the location alters the logic and can lead to different results.
Based on the above it is my recommendation your host make the changes. If your host is unwilling to help, I would recommend asking to be assigned to another tech or a supervisor. Most hosts are very helpful in this area. If the host is not willing to help, perhaps you can ask your web developer to make the change.
If you decide to make the change yourself I recommend you doing some online research into how the htaccess file works. You do not want to fly blind in this file.
Suggested reading: http://net.tutsplus.com/tutorials/other/the-ultimate-guide-to-htaccess-files/