I STRONGLY recommend you go to http://1-EFT.com and learn EFT (really easy and its free!).
Then make a long list of all your negative beliefs around not being smart (enough), such as, "I can't seem to learn maths easily" or "I do stupid things and that means I'm stupid" and tap your way through them all, one by one, over a period of time.
Also spot any limiting beliefs you have about your intelligence, day by day, and treat them with EFT as well.
If you do that diligently, I PROMISE you will improve your smarts, and quickly, too.
I BELIEVE IN YOU!
Like all humans, you have more neurons in your brain than there are stars in the visible sky, and the connections between them are to all intents and purposes, INFINITE.
You can learn, you can think, you are already much, much smarter than you think and you can get a whole lot smarter still!