How to remove Google Account that is set for Android Market in device? In my Device I have entered the the xyz@gmail.com as google account and I have also set that account as the Market account.
Now I want to use abc@gmail.com as my market account but I am not able to do that. 
So how to set that another account for the android market.

I also want to remove the account xyz@gmail.com from my device completely. That Account I have set at the First time in to my device and now I am not able to remove it from the Device.

So what should I have to do for it?
You can't currently remove the primary Google account that you used to set up your Android device, the quickest way to switch to your new Google account would be to restore factory defaults and set up your device to use the new account.

The location of the factory reset depends on the Android version of the device. On ICS (4.0+) devices it's in Settings -> Backup &amp; reset -> Factory data reset. On Honeycomb (3.x) devices it's in Settings -> Privacy -> Factory data reset. The same goes for Froyo + Gingerbread (2.0-2.3.x) if i remember correctly. 

Note that this will clear your apps and their data, and depending on your device, MAY wipe your internal and/or external SD card, as TryTryAgain mentioned.