how to delete a first row

if i have got 4 rows, i cannot delete thr first row using deleterow(rowindex),but i delete other rows . pls help me

If you are trying to delete the row selected 'highlighted', then try replacing:
// get the last row index
var i = obj.getRowCount() - 1;
with:
// get the last selected row
var s = obj.getSelectedRows();

But it need more REWORK on check-row-selection and fails on multiple selected rows.
There is good sample for that :
http://www.activewidgets.com/javascript.forum.12869.5/hide-show-rows-issue.html
Or you can also search for 'deleterow' in the forum to get more samples.
HTH