I need convert this http://bioval.jrc.ec.europa.eu/products/gam/images/large/access-map.png (is it robinson?) to Equirectangular (ESPG:32662) How can i get this using gdalwarp?
Since the png file has no georeferencing information, you have to georeference the file manually.
This is rather simple if you have QGIS, and use Natural Earth shapefiles as reference, or the Openstreetmap background from the Openlayers plugin.
Gdalwarp needs GCP ( Ground control points), and you get those with QGIS by just clicking on the image and on the reference background.