The correct answer is - individual organisms change their genes within their lifetime.
The organisms do not change their genes within their lifetime, If that was possible, than there was not going to be organisms that have gone extinct because of dramatic changes of their environment, as they would have been able to alter themselves in accordance to the environment.
The change in the genes, or the mutations, appear in the offspring. The experiences that the parents had over their lifetime, and the things that can be considered as advantageous, little by little appear in the next generation in order to make it more suitable to survive.