Click the "Edit" button in the lower right-hand panel (which is a square icon with a northwest-pointing white arrow beside zoom buttons). You can move and rotate all of your structures, but only Improvements can be permanently deleted once they have been built.
You can move and rotate all of your structures, but only Improvements can be permanently deleted once they have been built. If you find yourself running out of room, you may expand your Base by recruiting new friends to play or by spending Diamonds. You may also use the edit function to upgrade your defenses to higher levels.