Hard to know what to tell you to upgrade. Really depends on what you currently don't like. You mention the pedals, so there's a start. Do you find the current ones too flexy, or slippery? Good pedals make a difference, though there are some very good composite (not metal) ones out there. Look for ones with decent pins for traction and a big platform.
What kind of tires are on it? Tires are often the best bang-for-buck investment.
The better you can describe the riding you do on this bike, the better help you will get.
And pics help a lot as well.