If Document Owner
is a User field then using PowerShell would be your best approach:
Add-PSSnapin Microsoft.SharePoint.Powershell
$web = Get-SPWeb "http://server/sites/website"
$library = $web.Lists["Display Name of your library"]
$oldUser = $web.EnsureUser("DOMAIN\OldUserAccount")
$newUser = $web.EnsureUser("DOMAIN\NewUserAccount")
foreach ($item in $library.Items)
{
$userfield = New-Object Microsoft.SharePoint.SPFieldUserValue($web,$item["DocumentAuthorColumnInternalName"].ToString())
$login = $userfield.User.LoginName
if ($login -eq $oldUser.LoginName)
{
$item["DocumentAuthorColumnInternalName"] = $newUser
#if you are using default "Author" column, you need to set the following as well:
#$item.Properties["vti_author"] = $newUser.LoginName
$item.UpdateOverwriteVersion() #this saves changes without incrementing the version
}
$login = $null
}
$web.Dispose();