Sign in to Esri ArcGIS Online at: http://www.arcgis.com/home/webmap/viewer.html.
Open your map in the map viewer and click Add.
From the Add dropdown, click Search for layers.
At Find, enter Nearmap.
At In, select ArcGIS Online.
Select ArcGIS Online from the In drop-down menu.
Enter nearmap in the Find text box.
Click Nearmap US PhotoMaps for US customers, Nearmap AU PhotoMaps for AU customers, or Nearmap NZ PhotoMaps for NZ customers.
Click Use as basemap.
Click Done adding layers.
Save your map.
Close and re-open the map viewer page.
The additional Nearmap zoom levels will now be available for viewing.