Is change of Bitcoin address of an account possible? I have multiple Bitcoin addresses in my Bitcoin Daemon, 


Which address will be used for receive transaction
Can i change my default account address(mentioned in 1) to new one
Yes, you can generate a new address and use that to receive transactions instead. However, note that funds from the old address don't automatically get transferred to the new address, so don't delete the private key to your old address! If you always keep a copy of your wallet.dat safe (with backups), you don't need to worry about this.
The (default) thing is just a label. You can rename it to anything you want. There is no difference between the "default" address and a new one.