Well you could probably overclock that card with an application that will overclock that card. But if you're running that and much else of a system; I wouldn't suggest it at all. 220w is weak and shouldn't be used to power much more than a cpu/mobo/ram/HDD/integrated graphics.
how can I overclock my Radeon6570 graphics card with 220W power supply? Please help me and give me a solution.
you cant overclock ona cheap pwoer supply either it will just not be enough power for your card or you could literally kill the weak PSU and maybe some smoke will come out.
to tell you the truth im suprized your current card hasn't blown your PSU never mind overclocking it Trust me its not worth overclocking your Card and literally possibly killing your cpu ram and motherboard because thats what can happen with cheap power supplys they kill other stuff when they die dont risk it buy a New Corsair 430watt PSU then give it a try dnt forget to thumbs up if i was helpful