It is difficult to say how you can improve the performance of the controller in such a broad sense, for this case you can start by considering the controller as any other computer, it may be that reformatting or removing programs and services that are not needed could be beneficial.
It may be that the age of the controller itself is resulting in problems with its performance and that some maintenance would be needed.
How bad is the performance you are seeing for this controller, and how much use has this controller seen over time, is this a recent problem?