Follow these simple steps:

1. Go to Dashboard > Design > Add a gadget > Html/Javascript.
2. Paste these codes into the section:
<a title="Back to Top" href="#" style="position: fixed; bottom: 5px; right: 5px;"><img src="URL IMAGE"></a>

3. Substitute URL IMAGE with your own image URL.
4. Click Preview.
5. Save your template once satisfied.


Here are some images that you can use:


http://img338.imageshack.us/img338/9871/2evyotw.gif


hhttp://img132.imageshack.us/img132/5848/totopbutton.png


http://img175.imageshack.us/img175/7297/up3.png


http://4.bp.blogspot.com/_JwD5r652h00/SvDBWWig4UI/AAAAAAAAARI/
28cXbIDOaqk/s400/bttp-11.png


http://1.bp.blogspot.com/_JwD5r652h00/SvDBXF2WGRI/AAAAAAAAARo/
FIPZOwsTTBc/s400/bttp-15.png


Notes: This button is important for usability when the pages are too long.