How to access ftp via wordpress?

wordpress has it own opload tools for images and other 'media'.
But it uses ftp when you do an update.
What is not working for you?

thanks pzuurveen ,and I require ftp login via custom login form and then download the .txt file and display products in(.txt or .csv ) on wordpress site.or via simple php code how ican custom login into ftp

You can use any ftp-client to login to you wp-site.
Use the same username/password as when updating.

But if that cusom-form is on the same server as wp, you can simply use a simple webform to upload your products.csv

if not: ftp-put