As an example, the Ice Cream Parlor can be upgraded twice, with the first upgrade (technically to Level 2) coming after collecting from and supplying your Ice Cream Parlor 50 times. This takes the parlor's stats to 495 coins earned for every 100 Goods supplied (the default is 308 coins for every 70 Goods). Once that's done, you can complete the upgrade process all over again to reach Level 3, where you'll supply the parlor with 130 Goods and earn 660 coins in the process.
You'll need to complete similar tasks to upgrade the Sunglasses Store and Bike Shop, but remember, you can speed up your work considerably by asking your friends to help you out, rather than going it alone. Since the buildings don't change in appearance, these upgrades are fairly large no-brainers: if you've got the Goods to supply their higher demands, why not accept the higher payouts in return? As usual, we'll continue to let you know when more upgrades are released in the future, so keep checking back.
Which of these three business upgrades will you start first in CityVille? Do you own all three businesses already, or will you have to actually build one first so that you can actually upgrade it? Sound off in the comments.