You can change the way the palm tree looks by changing its size and the direction that it is facing.
To scale the palm tree (make it bigger), find the yellow sphere in the bottom corner of the box surrounding your selected palm tree. This may be difficult to find in the yellow sand, but it is there! Then, click and drag it away from the palm tree to make its scale increase.
To rotate the palm tree, notice that there are three curved arrows in the box around the tree. Try each one to get the appropriate rotation, and make the palm tree feel naturally in place.