To move, remove or sell objects, you'll need to enable movement mode in the main menu bar:
Simply click on an item to select it. You can click and drag it around to move it around.
The button with the swirled arrow at the bottom will let you rotate it. You can confirm the new placement by clicking on the green checkmark button.
To sell the item, just click on the red bulldozer button, and confirm the window with the red "Tear Down" button.
Note: Not all decorations and buildings can be sold!