Select the row below the rows you want to freeze
Go to the View tab
Click Freeze Panes
Click Freeze Panes from the dropdown
To freeze only the top row, click View
Click Freeze Panes
Click Freeze Top Row
To freeze only the first column, click View
Click Freeze Panes
Click Freeze First Column
To unfreeze rows or columns, click View
Click Freeze Panes
Click Unfreeze Panes