Don't. The idea of an IDENTITY field is that it's unique, but (deliberatly) not necessarily sequential. In practice, they are sequential, but SQL never "reuses" freed numbers when you delete records, so that any other systems or tables that reference the row via the field don't pick up the "wrong" data.
If you want a sequential number for your rows based on the Identity field, then use ROW_NUMBER and ORDER BY:
SELECT ROW_NUMBER() OVER (ORDER BY ID ASC) AS [Sequence Number], * FROM MyTable
That will always give you a sequence starting from 1 with no gaps.
"yes It is Giving but I want to display all in datagridview so that every time if user delets the record it will recount"
That's trivial! All you need is a column to put it in, and to handle the RowPrePaint event:
void myDataGridView_RowPrePaint(object sender, DataGridViewRowPrePaintEventArgs e)
{
myDataGridView.Rows[e.RowIndex].Cells[0].Value = e.RowIndex + 1;
}