To change your account name, you must create a new account. You can't simply change the name of your existing one.
To create a signature, visit a website like photobucket.com and set up an account. Then, click on the "my album" link. There, on the left hand side of the screen will be several buttons marked "browse" click on one. A window should pop up and it will probably be marked "My Documents". These are the documents on your computer currently. Open any folder that contains an image that you would like to upload to the site and double click it. This will place the image's location on your computer into the text bar. Click "upload" the screen will change and it will process your upload. The next screen you see should be one asking for a "tag" to make your image easier to find. Unless you have an extremely large album, this step is not necessary. Click the "next" or "continue" button. You will be taken to your album. When there, find the image you want and take the last code (there will be four). Simply click on the text and it will be copied automatically to your copy/paste. Then, go to the disboards and find the User CP tab. Click on that then click on "edit signature". In the text box, right click, then select "paste". Your previously selected text will appear and voila, signature.
If you don't have any images on your computer currently that you would like to use, simply do a google images search for them. Type a word relavent to your search into the search bar and when you find a picture you like, click on it. When you see the next page, there should be a link at the top that should read "See full-size image". Click on it. You will be taken to a page with solely that image on it. Right click, then "Save picture as". Enter a file name after selecting the folder you want to save it to. Then follow the instructions above.
Signature guideliines can be found
here.
If you need any other help, feel free to PM me. I'll answer you as quick as I can.