So you want to change this:
into something more like this:
On a normal bike this would be only a matter of getting the (common) parts and about 3 hours of work. However, notice on the second picture where the front derailleur is actually mounted - there's an extra little piece of tubing coming up from the bottom tube right above the crank. Your model seems to lack this. Because this bike uses such an odd design, getting a front derailleur onto your bike is next to impossible without some serious welding. If this sounds incorrect, please post some pictures of your specific bike and we can help you better.
The simplest option for wider gearing with just a single chain ring is to change the cassette. This is a common fix, but you will need to make sure that your rear derailleur can handle it. Derailleurs have a maximum difference in teeth that they can shift over, so you need to stay within this range if you're going to change the cassette. Also, if you just want to change the gearing in one direction, (faster, not easier, or vice versa) you can change the cassette to accommodate that or change the front chainring to be larger or smaller, as needed.