What should I do if I accepted a review request based on paper title, but then found out it touches on topics I don't know? I am a Phd student from Algeria, and I received an invitation to Review for the International Journal of Adaptive Control and Signal Processing. My Phd supervisor advised me to accept the invitation to review the paper, so I accepted the invitation. 

Now from the title of the paper, it looks to be in the field that I am working in. However, when I accepted the invitation and they sent the manuscript to me, it is much more complicated than it looks from its title and touches on topics that I do not know.

What are the best responses should I give in the reply?
You have two choices, each of which I have done at different times:


You can tell your advisor and the editors that now that you've seen the paper, you no longer think you could do a good job reviewing it. 
You can review it to the best of your ability and state clearly in the review that you have low confidence in your review. (Often, this can be indicated numerically.)