Final answer:
In SolidWorks, to rotate parts in an assembly, use the Rotate Component tool or the Move with Triad tool. Select the part and use the corresponding tool's interface to rotate it. Fully defined parts may require editing of mates to allow rotation.
Step-by-step explanation:
To rotate parts in a SolidWorks assembly, you can use either the Rotate Component tool or the Move with Triad tool. Begin by selecting the part you wish to rotate. Then, choose the Rotate Component tool from the Assembly toolbar or right-click the component and select "Move with Triad". If using the Rotate Component tool, click and drag the rings of the rotation sphere that appears to rotate the part around the desired axis. For more precise control, consider entering specific rotation angles in the Property Manager. If using the Move with Triad tool, you can drag the rotational handles of the triad to rotate the part around an axis.
If the part is fully defined (fully constrained) and cannot be rotated, you may need to suppress or edit the existing mates that restrict movement. Mates can be managed from the Feature Manager Design Tree under the Mates folder. Remember to save your assembly after making changes to ensure your rotations are retained.