Adding to the great info provided by José: you may have the need to hide the Delete option for certain rows only (leaving it enabled for others). If so, try the following...
Add this CSS to your theme:
.SelectedRORow + .RowControlGroup a.DeleteRowAction { display: none !important; }
Adapt and add this script to one unescaped expression (place it in one of the cells). Use a If widget to include it for rows that cannot be deleted).
"<script language='javascript'>
var row = $(""#" + ETable.Id + " input[id=" + UserExtension_Blog.Id + "]"").closest('tr');
row.addClass('SelectedRORow');
</script>"
Finally, don't forget to perform a validation when deleting the row (server-side), as CSS can be changed by the user in runtime.