Maintain AD via CSV import to change or Add users

Hi 

I'm very new to Powershell and i am looking to put together a script which uses a CSVfile to firstly check if an employee exists, if they exist then use set-aduser to update fields in AD from the details in the CSV .  If they do not exist then use Add_aduser to create the employee.

I can create employees with no issue using the script below but this doesn't cover all of my requirements.

Ideally i want the script to check the CSV for a column (Change_Add) which states Add (for new employee) or Change (to update details).

Please could you help or advise on how i might achieve this?

Thanks

###########################################################
# COMMENT : This script creates new Active Directory users
#           including different kind of properties based
#           on an test_user_access_form.csv.
###########################################################
Import-Module ActiveDirectory
# Get current directory and set import file in variable
$path     = Split-Path -parent $MyInvocation.MyCommand.Definition
$newpath  = $path + "\CSV\test_User_Access_Form.csv"
# Define variables
$log      = $path + "\create_ad_users.log"
$date     = Get-Date
$i        = 0
# Change this to the location you want the users to be created in your AD
$location = "OU=Users,OU=LAN,DC=company,DC=co,DC=uk"
# FUNCTIONS
Function createUsers
{"Created following users (on " + $date + "): " | Out-File $log -append"--------------------------------------------" | Out-File $log -append
  Import-CSV $newpath | ForEach-Object { 
    $sam = $_.sAMAccountName
    Try   { $exists = Get-ADUser -LDAPFilter "(sAMAccountName=$sam)" }
    Catch { }
    If(!$exists)
    {
      $i++
      # Set all variables according to the table names in the Excel 
      # sheet / import CSV. The names can differ in every project, but 
      # if the names change, make sure to change it below as well.
      $setpass = ConvertTo-SecureString -AsPlainText $_.Password -force
      New-ADUser $sam -GivenName $_.GivenName `
      -Initials $_.Initials `
      -Surname $_.SN `
      -DisplayName $_.DisplayName `
      -Office $_.OfficeName `
      -StreetAddress $_.StreetAddress `
      -City $_.L `
      -PostalCode $_.PostalCode `
      -UserPrincipalName $_.UPN `
      -Company $_.Company `
      -Department $_.Department `
      -EmployeeID $_.ID `
      -Title $_.JobTitle `
      -OfficePhone $_.StorePhone `
      -HomePhone $_.HomePhone `
      -AccountPassword $setpass `
      -Manager $_.Manager `
      -ChangePasswordAtLogon $true `
      -Enabled $true 
      # Set an ExtensionAttribute
      $dn  = (Get-ADUser $sam).DistinguishedName
      $ext = [ADSI]"LDAP://$dn"
      If ($_.ExtensionAttribute1 -ne "" -And $_.ExtensionAttribute1 -ne $Null)
      {
        $ext.Put("extensionAttribute1", $_.ExtensionAttribute1)
        $ext.SetInfo()
      }
      set-aduser $dn -Add @{ExtensionAttribute11= $_.ExtensionAttribute11}
      set-aduser $dn -Add @{ExtensionAttribute12= $_.ExtensionAttribute12}
      set-aduser $dn -Add @{ExtensionAttribute13= $_.ExtensionAttribute13}
      set-aduser $dn -Add @{DepartmentNumber= $_.DepartmentNumber}
      set-aduser $dn -Add @{ipPhone= $_.ipPhone}
 # Move the user to the OU you set above. If you don't want to
      # move the user(s) and just create them in the global Users
      # OU, comment the string below
      Move-ADObject "CN=$sam,CN=Users,DC=tgifridays,DC=co,DC=uk" -TargetPath $location
      # Rename the object
      $newdn = (Get-ADUser $sam).DistinguishedName
      Rename-ADObject -Identity $newdn -NewName $_.Displayname
      $output  = $i.ToString() + ") Name: " + $_.DisplayName + "  sAMAccountName: " 
      $output += $sam + "  Pass: " + $_.Password
      $output | Out-File $log -append
    }
    Else
    {"SKIPPED - ALREADY EXISTS OR ERROR: " + $_.DisplayName | Out-File $log -append
    }
  }"----------------------------------------" + "`n" | Out-File $log -append
}
# RUN SCRIPT
createUsers

Write-Host "File import complete please check log file for errors"
#Finished