What you should do is to use the chain rule. Denote the upper limit of the integral (the limit which itself is an integral) as y(x). Then you should be able to see that dF/dx = dF/dy dy/dx.
The general Leibniz' formula is
\frac{d}{dx}\int_{\alpha(x)}^{\beta(x)} F(x,t)dt= \frac{d\beta(x)}{dx}F(x,\beta(x))- \frac{d\alpha(x)}{dx}F(x,\alpha(x))+ \int_{\alpha(x)}^{\beta(x)}\frac{\partial F(x,t)}{\partial x} dt