Can I amend my sole proprietorship schedule C returns to qualified joint venture and for how many years?

My wife and I started our business 10 years ago and we've been 50/50 since the beginning.  We had an accountant who had us do a schedule C return with me as the sole proprietor and her listed as a homemaker.  I never understood the returns, nor did I pay much attention to it until I started learning more about taxes as a hobby.  Then, I learned that my wife basically has no social security earnings and when she retires she'll have no SS.  How do I fix this?