Where can I change FTP account password?

Control Panel V5 > Hostings > FTP
You can follow below steps to change FTP account password.
 
1. Login to hosting account control panel --> WEBSITES --> click "..." at the right of your site --> click "FTP Access" in "Basic".
 
2. In the pop up window, click "Add FTP User".
 
3. Choose the detail FTP account, click the pen icon under "MODIFY", then you will be able to change the FTP password.