I will try to help you being an AMD person myself. My last two (actually three) desktops were AMD, also my last laptop is AMD. My current system is AMD. You are trying to use the AMD Athlon 64x2 unlocked. Great processor, but it's a little dated. Your motherboard and DDR2 RAM is also dated. But you can try to overclock it. First off, what are you trying to overclock for? You "read" it makes your CPU better. Are you an average/casual PC user? If you like the way your PC is, there is no need to get into the headache and frustration of overclocking. It's not easy and takes alot of trial and error, sometimes even to get just a CPU to 2.5Ghz.
But there's the plus sides. Is your computer a little sluggish? Or you trying to game with this (I'll get into that below). You should be able to bump your's up to 2.5Ghz VERY easily. Just go into your motherboard's BIOS. Depending on your configuration, you can either increase your CLOCK MULTIPLER or increase the FSB (front side bus multiplier) UP so it increases your processor, you should see the number physically go up in my BIOS. Increasing the clock multiplier will affect only the CPU, increasing FSB will increase other things like your RAM speed. Just increase it just enough where the CPU speed is at 2,500Mhz (2.5Ghz) and nothing more, it's okay if it's 2,513Mhz or not exact. Don't worry about the voltage, you have enough to get an extra .3Ghz out of it. Go on the web or youtube and look for tutorials that are more specific.
If you don't have these kinds of settings in your motherboard then I'm afraid you can't overclock your CPU. Some motherboards are locked and that ASUS model you're sporting might be because I had something similar in my last setup. Might you take my recommendation, though... if you are looking for a serious performance increase or for gaming, you should upgrade this system. That CPU is over four years old, DDR2 is very outdated RAM it's hard to find anything for DDR2 anymore. For the numbers you are overclocking to, you're hardly going to notice any difference, you would want to aim for something like at least 3Ghz and I Don't know if that CPU is capable of that. On ebay, I got my motherboard/CPU for $180 bucks, it was a MASSIVE increase in performance. They bundled in an AMD six core processor for way less than market price. IF you just want to upgrade the motherboard even, you can get an AM3 board for under $100+ and that CPU you have would mostly likely even work in it (no guarantees but most are backwards compatible in the AMD department). Good luck.