You can remove the assembly relationship between individual elements in a selected assembly at any time. The disassembled elements remain in the model. Other instances of the same assembly type are unaffected.
If the assembly that you disassemble is the last or only one of its type, then that type and any of its associated assembly views are removed from the project.
- In the drawing area, select the assembly.
- Click Modify | Assemblies tab
Assembly panel 
(Disassemble).