You can change FTP password from cPanel using following steps:
- Login to cPanel.
- Go to the 'FTP Accounts' in 'File' section.
- Scroll down and look for your user.
- Select 'Change password' from the drop down menu in the 'Functions' column.
- Next screen will ask you the new password. Supply new strong password two times (password and confirm password).
- Click 'Change' button.