Mail Chimp: Upadting user's details using ListUpdateMember

http://us2.api.mailchimp.com/1.3/
?method=listUpdateMember
&apikey=#######################
&id=mylistid
&email_address= "current_existing_email"
&merge_vars[FNAME]=firstname
&merge_vars[LNAME]=lastname
&merge_vars[EMAIL]=" New_email "
&email_type=html
&replace_interests=false