How can I change the frame in the print composer in QGIS?

I made a map based on a raster from Natural Earth web site with some vector layers with the Qgis software. When I compose this map I cannot get the right size: there are too big or to small as you can see in the photos. I tried to change all the setting in the composer, but does not work.

Can anywhere, please, can explain how to crop the frame in the composer so I can get rid of the white border?

Answer

There is Resize page to content option in Composition tab (QGIS 2.18). You can set the margins and click on the Resize page button.