Updating Data by Adding Files to Sharepoint Folder

Hi all,

I'm a noob, and I'm hoping that my workflow will work as follows. 

1. Add my data, which includes dates and some other metrics, to a sharepoint folder.
2. PowerBI pulls the data from the sharepoint folder based on a query I set up.
3. Moving forward, I add NEW data to this dashboard by adding new files to the sharepoint folder.

There will be some cases where the dates of the old data and new data overlap. Let's say this data includes engagements with a tool. Originally the engagements on one past day may be x, but when I drop in the new data, the engagements may have changed to y for that same past day. How will PowerBI react to this? I would like PowerBI to update the data to reflect the newly added data and disregard the old stuff.

I would prefer to not have to go in an manual scrub the old sheets whenever I add files to the folder.

Let me know your thoughts, and thanks in advance.