If you want to change primary FTP Account which shares the username with the cPanel login, then you need to change the password of your cPanel Account. However, if you want to change the password of a specific FTP Account, you may follow these instructions.
1. Log into your cPanel account.
2. In the "Files" section, click on "FTP Accounts" Icon.
3. Under the "FTP Accounts" list, click on "Change Password" or use the "Password Generator". 
4. Click on the "Change Password" button.
Now you can access your FTP user account with your new password.
