I don't think replacing it could lower the temperature; you probably have a ventilation problem. What are your full specs? Can you post a picture of your case/ventilation setup?
There's my set-up, here's my case.http://www.newegg.com/Product/Product.aspx?Item=N82E16811119160
The top fan is blowing out, side fan is blowing in, and CPU fans are blowing in, through that radiator. So hot air is coming in from the CPU fans.
EDIT: Even if I remove my second card the temps are still high.