I assume you are using the latest cPanel with the x3 skin (you will be if your on shared hosting here). To change your password go to the Preferences section at the top of cPanel and click the "Change Password" option to change your main password.
You can use software such as Dreamweaver, Expression Web, Frontpage, Word or even Notepad to create a .htm or .php file. Frontpage isn't the best software in the world but normally the easiest for beginners.
If you just want to type in the code you can create a new .htm or .php file through file manager and save it over the original index file there.
Hope that helps
. If you have any more questions feel free to post again and I will try to answer them as well as possible!