To perform a bulk update on your members, you first need to export them on the "Members > View Coaches/Members/Parents" page. Click on the EXCEL button.
Once you have the exported file, edit the file then go to "Members > Bulk Update".
If you are only updating one or two fields, you can safely delete all other columns except the first one (System ID) and the column(s) you are updating.
If you receive the error "System can't read file, please check there are no blank columns", try the following:
Open the file in Excel and press "Ctrl + End (the end key)". If the active cell is past the last column in the spreadsheet, select a few columns after the last one and delete them. Then try again.
See the image above. The active cell is 3 columns past the last column (BX). What this means is that there are "blank" columns after the BX column that need to be deleted.