Swapping up brakes on an inexpensive bike is not a great idea- expensive and possible compatiblity problems. A good wrench can adjust them, and usually you can switch to better brake pads for a reasonable amount of money and a lot more stopping power. The factory pads are probably Shimano Black ones, and they're lousy. Even dialing out the barrel adjusters will help sometimes. Ask the guy at the LBS what that is.
Cleaning the rims will help too- Windex is best for that. Brake pads will slide on grit and chew up the rims. Cheesy pads will get grit embedded and slip on rims too.
Hope this helps,

Lizzy