I have a patent, and I can apply for invention patent and utility model patent. Which one should I apply for?

Of course, both are applied together. If the application is practical, it will be authorized in a few months. First, some technologies will be protected and products will be used first. The application for invention can be protected for another 20 years, but it costs more and is the best. After you get the invention certificate, you don't need to be practical, and you don't have to pay the annual fee for practical patents. In case there is no invention certificate, at least a practical certificate can be used.