Hi Balaji,
fslswapdim (a command line program which comes as part of fsl) should solve your orientation problems. If you have fsl installed (which you should do!) then typing fslswapdim input_volume_name -x output_volume_name into the terminal should swap RAS to LAS and vice versa.
Or you can just type in fslswapdim into the terminal to get help.
Best of luck!
Sean