This page will explain how to change a basemap for a web map in ArcGIS Online (AGOL)
In AGOL, navigate to your Group page

Press the "Content" tab in your Group page
Find and select your Collector Map (Organization Name)

Press the "Open in Map Viewer" button

See the Map Viewer with the Collector Map (Organization Name)

Press the "Basemap" button

Choose your desired Basemap
Note see the difference in the two Basemaps

Press the "Save" button
