can any one tell me how to change current shell's pwd ?

Type:

    cd /path/to/new/directory
[download]

at your current shell's prompt.

Be very, very glad that processes can't change the current working directory of other processes. Or else you would need to check your working directory each and every time your program called another program. Not to mention that doing a 'chdir', or accessing a file using a non-absolute path would be wrong between doing a fork and its matching SIGCHLD, as the child process might have changed the current working directory of the parent.