RemoveAdminAddNewAdminUser.ps1

$propADComputers = Get-ADComputer -Filter * -SearchBase "Whatever you want"
$name = Read-Host -AsSecureString "Enter the name of the non-built in admin you would like if required:"
$password = Read-Host -AsSecureString "Enter the password of the non-built in admin account you would like if required:"
foreach ($c in $propADComputers | Select-Object -ExpandProperty "Name")
{

    try{

        #Start remote PSSession to PC
        Write-Host "Attempting to enter PSSession for $c..."
        Enter-PSSession $c
        Write-Host "Success!"

        #Local Built-In Admin Account & account information
        Write-Host "Fetching built-in admin account..."
        $builtinAdmin = Invoke-Command -ComputerName $c -ScriptBlock {Get-LocalUser | ? {$_.SID -like "*-500"}}
        $name = ($builtinAdmin | Select-Object -ExpandProperty "Name").ToLower()
        $isEnabled = $builtinAdmin | Select-Object -ExpandProperty "Enabled"

        if($name -contains "$name"){
            "Built-in account name is $name...let's change it"
            Invoke-Command -ComputerName $c -ScriptBlock {(Rename-LocalUser -Name $using:name -NewName "Administrator")
        }
        if ($isEnabled -eq $True){
            "Built-in account is enabled...let's disable it."
            #Need to run it again to get the new name
            $builtinAdmin = Invoke-Command -ComputerName $c -ScriptBlock {Get-LocalUser | ? {$_.SID -like "*-500"}}
            Invoke-Command -ComputerName $c -ScriptBlock {Disable-LocalUser -Name $Using:builtinAdmin | Select-Object -ExpandProperty "Name"}
        }
        Write-Host "Creating non built-in admin account..."
        Invoke-Command -ComputerName $c -ScriptBlock {
            (New-LocalUser -Name $Using:name -Password $Using:password -PasswordNeverExpires), (Add-LocalGroupMember -Group "Administrators" -Member $Using:name)
        }
    }
        Exit-PSSession
    }
    catch{
        Write-Host "Unable to enter PSSession to $c"
    }
}