How do I overwrite an old data set in SpatialKey, instead of it creating a new data set?

When a data set is pushed over to Analytics, it's essentially being passed in spreadsheet form. If you upload the same data set without changing the fields, it will automatically overwrite the previously-imported data set. However, when fields are added or removed, it changes the spreadsheet columns and the underlying layout, so a new, duplicate data set is created. When there's a difference in records (or rows on a spreadsheet), it doesn't affect the layout of the spreadsheet. 

If you have custom Analytics reports/dashboards that are affected by this process, you can take these steps to ensure you don't lose your saved report: Import the new data set, then open your existing report in Analytics. Bring the new data set into the report and set it up so it is identical to the old one. Finally, remove the old one and re-save it before you delete that old data set. That will ensure you don't lose your saved report.