Here it depends on whether you are using the Confixx or Plesk control panel.
Your web user webXXX (eg web123) is also the user name for logging into the Confixx control panel and for the FTP connection. So if you change the password, you change both accesses at the same time.
You can therefore change the FTP password in the myhosttech customer center under “Servercenter” by clicking on Change password (FTP & Control Panel) in the settings for the corresponding product.
It may take 20 minutes for the change to take effect.
In the Plesk Control Panel you can click on FTP access under “Websites & Domains” on the left under your domain. Click on the user and enter the new password twice.