Is there any option to change design on stackexchange sites?
Current school notebook-like theme is not good.
This is the theme for Beta sites. Once a site leave Beta, a new design will be designed for the site.
There is no way to change the theme unless you apply a user stylesheet.
I just want to echo what waiwai993 said and add a little something:
If you don't like the current beta theme, you are free to propose an alternative style to be used when the site goes out of beta on the site's Meta. Jeff has stated something, somewhere, about Jin Yang designing the site's style, but I'm sure if the site's community knows what it wants and one of them can supply it, then there will be no hesitation to adopt it.