Here is a link to buy the right supply for you: http://www.lmgtfy.com/?q=12V+2A+power+supply
Not easily - and impossible to answer without more information.
Buy a new power supply.
i am having 12v dc 500ma output.but i need 12v dc 2a. is there any possibility to convert these 500ma to 2a ?
No I am sorry - To get more current you would need to lower the voltage - You need another Power supply.
There is no way to convert 12V*500mA=6W to 12V*2A=24W.
Buy a new supply.