The only reason to do it backwards is if you do not plan to keep track of
the deletions or do not want to try and work out the new end condition.

To delete the 3rd to 6th row you can

For i = 6 to 3 Step -1
Worksheets("Sheet1").Rows(i).Delete
Next i

Or

j = 3
For i = 1 to 4
Worksheets("Sheet1").Rows(j).Delete
Next i

Which is the same as:

Worksheets("Sheet1").Rows(3).Delete
Worksheets("Sheet1").Rows(3).Delete
Worksheets("Sheet1").Rows(3).Delete
Worksheets("Sheet1").Rows(3).Delete