Fisher Information is defined as $I_{\lambda}=E[(\frac{\partial f(y,x)}{\partial \lambda})^2]$.
I want to show that $I_{g(\lambda)} = I_{\lambda}(g'(\lambda))^2$.
All I managed to do is
$I_{g(\lambda)} = E[(\frac{\partial f(y,x)}{\partial g(\lambda)})^2]= E[(\frac{\partial f(y,x)}{\partial \lambda} \frac{1}{g'(\lambda)})^2]$
This might be a simple mistake, but is this wrong? It seems not to give the desired result...
The correct property is : $$(g'(λ))^{2}I_{g(λ)}=I_λ$$
So your steps are correct, but your initial goal was wrong.