IwubCheeze: To do that, you just need to buy land from the bank. To do that, click the globe icon on the left side of the screen and it will take you to a screen shown in the screenie attacted to this post. Click the plot of land you want to buy, click the buy icon and viola, new plot of land to expand your city :)
Keep in mind that in order to buy land your total land usage must be 90% or higher (you can check this stat in your headquarters), you must have no outstanding tax bill and you must have at least one house on each plot of land.
Happy building :)
tinyE: I was JUST logging on to tell you I found that option. :P I normally don't play these type games but I have become totally addicted to this one. I may be back with more stupid questions which judging by your avatar may not bode too well. :D
Haha, no worries, some of the older games had strange mechanics that weren't very intuitive and constructor is no exception. You'll still be finding things out like what certain kinds of tenants like and don't like, a balance between rent and making babies (I'll bet you anything you'll have problems either making too many babies or not enough, I had the same problems when I first played but I got it figured out now, heh heh :P), planning how to use your land etc etc. If you have any questions, don't be afraid to post, some of thse things I figured out with a lot of experimentation.
As for my avator, I wouldn't worry about it. Lets just say I break my own rules at times ;)