Update User Credentials using SharePoint Management Powershell

#Set Execution Policy
Set-ExecutionPolicy -ExecutionPolicy Unrestricted -force

#Import SharePoint Module
Add-PSSnapin Microsoft.SharePoint.PowerShell -EA silentlycontinue

$m = Get-SPManagedAccount -Identity "SHAREPOINTDOMAIN\spdb"

Set-SPManagedAccount -Identity $m  -ExistingPassword (ConvertTo-SecureString "Test@abc" -AsPlainText -force) –confirm