Thanks goes to DiGGer for writing this tutorial.
Follow these points to do it:
1. Make a banner that is 960(w)x160(h) in size or resize your banner to be that size. Either have your banner on a transparent background or the color of the background used on your page. Save the file as a PNG or JPG file.
2. Upload your banner to a free image hosting site such as Imageshack.us
and once the image has uploaded click on it and copy the "direct link".
3. Go to your dramatube user page and click on the "theme" link.
4. Scroll down and click on the "Advanced" tab.
5. If you see any code in the box, highlight it all and delete it so the box is empty.
6. Paste the following code in the box:
Delete the URL in bold being sure to leave the parenthesize " ( )
" and paste in the one you copied from Image Shack then click on the "Save" button. When you now view your dramatube user page the dramatube banner should be gone and in the place of it will be your banner.