I have core2duo e4500 @2,2Ghz and I want to overclock it to at least @3GHz, but my motherboard doesn't support overclocking. so, what do I do ?
You'd need to get a board that does support overclocking, you'll probably also need a decent aftermarket heatsink. But, given the age of the system the cost really isn't worth, it unless you have money to throw away and just want to see if it can be done.
Get a better mobo that can support OC activities, and some aftermarket cooler like, Cooler Master Hyper 212 EVO Cooler for instance, you can get that speed with good stability for sure.