please help as how to schedule a date

[get]

friends I have filled online ds 156 and 157 forms and saved my application ,
but I want to take a date as early as possible ,I have left some columns blank in the form which I want to fill up after some days is this possible .
can I confirm application and take a date and then change the details in the form later ?

how many times we can rechedule ????
am from hyderabad but I want to attend interview in delhi ,is it possible ,


please help me