There are two ways that you can edit information about an existing place on your Map:
1. Once you have drawn a place you can enter information about it by clicking on the place on your Map. A window will open that looks like the image below.
Next Click onto open the Edit Place form.
2. You can add also update information about an existing place by clicking on a place in your Places list in the Places Tool (see below):
Click on the place you would like to edit and its Overview tab will appear. Then click on the pencil icon next to the places name to open the Edit Place form:
Once you have opened the edit places form you can update any information for you place:
One important thing to note about editing your place dimensions is that when you draw your place on the map, the dimensions of your place are calculated from your drawing and are then added by default to your Total area and Tillable area which you can see in the above image in the Dimensions section.
However once you open up the edit form, you can edit your Total area and Tillable area, if the dimensions calculated from your drawing on the map were not perfectly accurate.
To learn more about how to draw and calculate your field acreage on the map check out this article link.