Bigger Bike

It was just two years ago when we bought our son’s bike and now, he may be needing the bigger one. I already adjusted his bike seat into its full height. I disassembled my wife's bicycle and now planning to assemble it again maybe with new parts to be replace some parts like chains, breaks and I am still searching for a types of grips fitted to that bike. Repaint it and hopefully my son can now use it.