You just added a new user account on your hosting environment, you configured it for ftp access, but it can not modify files.
That's just a permission issue.
All files of your hosting account belongs by default to the owner of the account, and their permission are read/write for the owner. Sometime read is configured, but write access is by default not allowed for the group and world.
Your new user belongs to the same group than the owner of your hosting account. To allow it to modify files, you just have to allow the write permissions on the group permission section of the file you want to grant access to.
If you are using an ftp graphical interface like Filezilla, this is very easy:
- Connect on you account with your management user via ftp.
- Select the file or folder you want to modify permission.
- Edit the file attributes, and make sure read and write of the group section is activated.
Modifying the permission of your system can prevent it to work correctly or decrease security level.