Return your bike at once.

Go to a local bike shop and buy a $350 mountain bike that will last you a lifetime.

Sorry to say it, but you just wasted your money. When you buy a bike at walmart, you will spend about twice to three times as much money you spent to actually get it working correctly.

It's not worth the money to upgrade it, since everything on it is worthless.

Again, I'm sorry to say but you should return it. I run around town assembling bikes for a living and I assemble at 3 different walmarts in my area and there is not a bike worth the time and money to buy. I've been doing this for 3 years, and I still can't get half of them shifting correctly, but the manager still makes me place them out on the shelves and they still sell regardless.