my teacher has given us this integration

$\displaystyle \int_0^x \frac{2. \lambda exp(- \lambda.x}{(1+exp(- \lambda.x)^2} dx$

I dont get how this equals

$\displaystyle \int_\frac{1}{2}^{\frac{1}{(1+exp(- \lambda.x)}} 2 du$

the domain of integration can change? can anyone explain this me?