Linux FTP user

Hello,
How can I create a FTP user with writing privileges ? The FTP user FreePBX gives me is READ Only.

What I need do is upload an audio file every day. The FreePBX IVR module plays this audio file on inbound calls but i need to upload a new version of that file every day.

It can be via FTP or any other way FreePBX / Linux allows me to.

Thanks,

Newbie