There are many ways of doing it.
With positive sentence:
Thank you, for I've become smarter. (accepting his help yet you might have done it yourself too)
Thank you, for making me smarter. (accepting without his help you wont be able to)
Thank you, I feel smarter now. (asuming the help you receive was only a small impact)
Same as above:
Thank you, for I've become wiser.
Thank you, for making me wiser.
Thank you, I feel wiser now.
With negative sentence:
Thank you, for making me less stupid. (sarcastic)
Thank you, I feel less stupid now. (sarcastic)
Other ways to imply that they showed you a new route to do things:
Thank you, for changing my perspective. (you could have found it yourself but the help is appriciated)
Thank you, for changing my way of thinking. (you were stuck this help was usefull)
Thank you, for changing my way of seeing things. (same as above "stuck")
Help was unnecessary but accepted:
Thank you, for your addition to my knowledge. (careless)
Thank you, for your addition to my library. (sarcastic)