Select the cell or cells with the drop-down list
Go to the Data tab
Click Data Validation
In the Settings tab, check the Source field
Edit the list items directly if they are typed in the Source box
If the source is a cell range, change the values in that range
If the source is a named range, update the named range in Name Manager
Click OK to save the changes
Copy and paste the updated drop-down to other cells if needed
Remove the drop-down by clearing Data Validation if you want to replace it completely