If I tweak a free web design protected by Creative Commons, is still copyrighted?

I’d like to use a free web design template I found, but the Creative Commons license says I have to leave the designer’s link on the website. If I am tweaking the design (color, size, layout, etc.) is the design still protected under this license?

In other words, how far does the design need to change before it stops being the original copyrighted material? Or does it ever?