changing exp to any value would not be too different from changing any other value, making 2x 4x etc would be very different.
To change exp you find the memory address that has the exp value. You see you exp is say 230 you search for 230, when you find it you just edit it. You just need to understand how to use a single tool, for example edizon se. Only requires average intelligence and moderate effort. Most fifth grader can learn to do it.
To make exp gain at 2x you find the code that manipulate exp, modify the code to give 2x exp. You need to understand assembly language and you need to be able to write assembly code. You also need to understand how to use multiple tools. Require above average intelligence and considerable grit. No way a simple guide can teach you this. Perhaps hire xtatu as your tutor? He looks like the expert on this topic.
I really appreciate your comment. Looks like it's very hard for an amateur can do those code.