When using MS Excel as a datafoundation, it is not possible to update the excel-sheet and hence update your story - you will have to build a new model, and replace that model in your story.
I will show you how this is done, in a simple and easy way.
First you should build a model, based on your excel-sheet - here is my sales-file on fishing rods for Jan and Feb:
And my model:
I create a story:
I reopen my Excel-sheet and add my sales for March and April:
In the "Data Management" tab in my model, I choose "Import Data From" a "File"
And I choose my updated Excel-sheet.. If all the fields are not mapped, I would have to map them manually by dragging and dropping - but since it is the same Excel-sheet - SAP Analytics Cloud does the manual labour for me - I choose the Import method: Clean and replace selected version data - to ensure that data is being deleted and reloaded - this resembles a full load in SAP BW.
And then I updated my story:
And I get the sales data from March and April in my story.
Conclusion:
By using this easy update functionality, you can actually update your story if it is based on a MS Excel sheet, and you can also blend this data with eg. SAP BW-data, without having to persist this data in SAP BW or other databases.