Cannot delete Column from List

When tried to delete some columns from list using GUI, Some of them don't give me option to delete.
Problem: I Can't delete column if it is sealed, hidden, or readonly
Solution: Change values of these properties to false before trying to delete

You can use PowerShell to change these properties and remove column from List like below:
$web = Get-SPWeb -identity SiteUrl
$list = $web.Lists[listName]
$column = $list.Fields[FieldName]
$column.Sealed = $false
$column.Hidden = $false
$column.ReadOnlyField = $false
$column.Update()
$list.Fields.Delete($column)

SharePoint Batch Insert/Update/Delete Performance

When you want to do bulk transaction insert, update, or delete.
If you have to update a larger number of items its highly recommended to not use the Update method on every item. Instead – use the batch update function ProcessBatchData provided by SPWeb.

StringBuilder query = new StringBuilder(); for (int itemIx=0;itemIx<100;itemIx++) {   query.AppendFormat("" +           "{1}" +           "New" +           "Save" +           "{2}" +        "", i, listGuid, someValue, "urn:schemas-microsoft-com:office:office#"); } SPContext.Current.Web.ProcessBatchData("" +     "{0}", query.ToString())

For more details of using ProcessBatchData check url:
http://stefan-stanev-sharepoint-blog.blogspot.com/2009/07/tips-for-using-spwebprocessbatchdata.html