You need to add Microsoft Excel x.x Objects to the project references.
Then it depends a little on how many sheets, which one etc. but basically
Dim xApp As New Excel.Application
xApp.Workbooks.Open ("C:\filename"
xApp.ActiveSheet.Cells(1, 5).Value = "E1"
xApp.ActiveSheet.Cells(1, 6).Value = "F1"
xApp.ActiveSheet.Cells(1, 7).Value = "G1"
xApp.ActiveSheet.Cells(1, 8).Value = "H1"
xApp.ActiveWorkbook.Save
xApp.ActiveWorkbook.Close
Set xApp = Nothing
Would set the first row E-H to those values. The cell coordinates could be variables in a loop etc.