$domainServer = 'ad1.mydomain.com'

$user = Read-Host -Prompt 'Last Name: '

get-aduser -f {SurName -eq $User}

$username = Read-Host -Prompt 'Username: '

$password = Read-Host -Prompt 'Password: '

Set-ADAccountPassword -Identity $username -NewPassword (ConvertTo-SecureString -AsPlainText $password -Force) -Server $domainServer