To create a drop-down list, select cell where you want it to be (in this case, cell I2), and in the Data tab on the ribbon, click "Data Validation" in the drop-down option with the same name.

Microsoft Excel: How to Remove a Drop-Down List. ... The Data Validation window minimizes and you go to the location of the menu options. Delete them all from the spreadsheet.

Choose Validation from the Data menu. In Excel 2007, click the Data tab and choose Data Validation from the Data Validation option’s drop-down list (in the Data Tools group). Click the Settings tab.