Resizing Background Image back to default

Hi;
Firstly, i am a complete doofus re WP and it`s workings. I set up a site with the theme:

DragonbeadsthemeSalesLtr 1.0 by Anonymous JettDigitals.com-generated theme

then added an optin form that was SUPPOSED to be a drop down – it obviously was not, and after uninstalling it, the background image of the above template has gone mad.

It has misaligned and created itself a huge space on the right hand side, making the site look terrible, and causing slow loading.

This problem persists even after activating other themes.

I am at the point of pulling out what is left of my hair, as I would like to launch this new site but cannot until this problem is resolved.

Is there anyone out there who can assist?

Many thanks,

Ozra