For version 1.22.6 and higher: To edit, find the decoration that you would like to edit. Then tap on it and hold until the green circle stops spinning. You will be prompte to select from three or four different designs and once you make a selection, tap the check mark button on the right corner.

For versions below 1.22.6: First, tap on the hammer icon in the bottom left of your screen. Once you've done this, an icon should appear over the furniture you would like to change. After tapping on the icon, you'll be able to choose from the available designs. Tap on the design you would like, and press the check mark button to confirm your selection.