The main thing to remember when performing Delete, Insert, Update, or Upsert operations is it only matters which rows of data your current selection spans across.
For example if you pulled a report on all the accounts and only want to update the first two, drag the selection rectangle so that any number of cells in the first two rows are selected (you may only select two cells, just make sure that these cells are located in different adjacent rows, if you select two cells in the same row, only one record will be updated).
Select Delete All/Insert All/Update All/Upsert All command to Delete/Insert/Update/Upsert all records in the spreadsheet. Be careful with this one though, these functions determine the used range using excel’s !UsedRange command, which is not always correct. Especially if you pulled a report and have some footer information at the bottom.