The net charge of an isolated system remains constant. The only way to change the net charge of a system is to bring in charge from elsewhere, or remove charge from the system.
Charge can be created and destroyed, but only in positive-negative pairs.
Two identical metal spheres are charged. Sphere A has a net charge of +7Q. Sphere B has a net charge of -3Q. The spheres are brought together, allowed to touch, and then separated. What is the net charge on each sphere now?
When the spheres are touched the net +4Q charge will spread out evenly over the two spheres. Each sphere will have a net charge of +2Q.