Replacing a data in a data file

I have a .csv file saved with firstname, lastname, address, phone informantion. when form is loaded, the firstname and last name will be loaded into a list box, the address and phone will be loaded into an array, when i click a name in the list box, all information about this person will be populated into four text boxes, then i do some changes in the text boxes. How can i save these information back to .csv file and replace the original one.


Thanks

I'd read in the complete file into memory and write the complete file with all changes (insertions, deletions and modifications) when the user hits the Save button.