C#, How to give system permission to a process which is already running?

You are very welcome.
—SA

By the way, as I can see now, I answered your previous question. This is how a process can be elevated. Not during runtime. Also, if you start a child process by a process with elevated permission, that child process can get the same or less permissions, but not the other way around. :-)
—SA

These are two different questions. You cannot directly find a parent process, but it's possible to figure out indirectly by look up of all processes. I don't remember further detail; it's easy to find out and almost never needed...
—SA

Even though, Sergey here understands Russian and you can surely use it. But there are others here who may use Google Translate to completely kill the mere purpose of your message.

So, use English as most of us here are able to understand English and would love to share their experiences with you! :-)

No offence to both of you guys here...

Apart from what Sergey has said above, putting it simply is just like a person. Once a person is born in a state, you cannot just update their "Nationality", "Race" and other details that easily.

When a process is started, PCB (Process control block) is provided with the details for that process, it holds the details for everything about that process in advance. Which resources it can use, what permissions it hold, the PID and other similar stuff.

If process would simply change their permissions on run-time, malware based programs would simply update their permissions set and execute the programs on a permission level that may render dangerous for the user, such as they might delete the data or at worse render the machines useless.

That is why, once a process starts, you cannot (even if you can, you should not!) alter the process details. Start a new one.