My processor is the AMD Athlon(tm) 64 X2 Dual Core Processor 6400+ and my mobo is an ASUSTeK Computer INC. (Asus) M2N-SLI. I'm just unsure how to change it to something else, or if my processor can even do it.
You are restricted to 95w phenoms. Your board can't run phenom II's, even with a bios flash. If you want to stick with amd and run a phenom II, I suggest a 790gmh chipset board with onboard video, which works with your old pc6400. If you have pc5300 or slower ram, then get a ddr3 board and upgrade your ram. Never changed out a board before, then read some faqs. If you decide to upgrade, list your board and cpu on craigslist for around $80; or you might get more on anandtech's for sale forum.
i'm not sure i understand the question here, it just says what type of system you have and the title just says "change from single channel" Do you mean that you want to use dual-channel RAM instead of single channel?
The CPU can run memory in dual channel. In order for that to happen though you need to have at least two memory sticks of the same size and preferably of the same speed, timings, and voltage. If your sticks are not meant for dual channel, you may have to raise the voltage and or loosen the timings in order to ensure stability in dual channel mode. Make sure to run memtest for a while to be sure that your RAM settings are safe and stable. If you don't know what memtest is then google it.