Single Track Elements or Objects
Select the element. Two circles appear. One (the concentric double circle) defines the center of rotation, the other one the rotation angle.
Rotating a collection of tracks
Select the track elements.
If you want to connect the tracks to a free connector of an existing track (most common case) you can do this by drag and drop.
If you want to chose a different angle, you can cut and paste the elements, als long as you did not confirm the new position with the left mouse button, you can rotate the elements with the keys K und L. The rotation angle per key press can be chosen in the Plan properties tab.