While update farm credential,if you get error -
"Error deploying administration application pool credentials. Another deployment may be active. An object of the type Microsoft.SharePoint.Administration.SPAdminAppPoolCredentialDeploymentJobDefinition named "job-admin-apppool-change" already exists under the parent Microsoft.SharePoint.Administration.SPTimerService named "SPTimerV4".
First check the -
timer job definitions, if there is any instance of SPAdminAppPoolCredentialDeploymentJobDefinition job. For that you need to check for below entry in timer job definition
If this entry exists, delete this entry. Try to update the password.
If it still not working, Second thing to check if for Time job
Go to Services -> stop sptimer job service -> update credential -> start service.
Now try to update the farm credential.