Step 1: Open the Build Menu (From the Bottom Right Corner of your screen)
Step 2: Click on the expansion you would like to purchase (currently, only 12x12 is available).
Step 3: Choose the area of land you want to expand into. (Choose wisely, i would recommend towards the bottom Right side of the City, Thus in few week you will be able to expand your city towards shipyard (Which is currently Locked).
Step 4: Click to confirm your choice.
After all done! one small pop up will come saying, "Your City Is Bigger! Now you have more room for businesses, houses & decorations!"
Click Okay! Done! Enjoy this by sharing 50 Goods to your friends!