C# Dynamically Load An Assembly And Use It And Then Unload it

I'm working on a plugin where the shell dll invokes methods in several other function dlls. Because we want to replace these function dlls during updating, the shell dll has to dynamically load those dll, and when updating, dynamically unload them.

I can do the load and unload part with AppDomain, but I can't find any resources about how to create an instance of a type in the loaded dll and invoke method on it. I'd be very much appreciate it if anyone can elaborate on this...

Thanks!