A lot of it will depend on how old the computer is. They added memory to the computer I use at work, and the guy from IT turned the computer off, opened the case, added the memory, closed the case and turned it back on. He was in and out of my office in less than 10 minutes. The computer is a Dell with an i3 processor.
Many computers of the last 10 years or so are plug and play, so adding things is relatively easy. I suggest going to the computer manufacturer's website to see what they have to say and perhaps contacting their tech support, if necessary.