How to render a big image

How can I output big images(much larger than the resolution of your monitor) ,please.Thank you guys!

Have a look at , it goes over it in detail:

.unrealengine.com/latest/INT/Engine/Basics/Screenshots/index.html#highresshot

You can also do it in the editor:
http://www.tomshannon3d.com/2014/07/awesome-ue4-tricks-1-take-screenshots.html

Ths a lot!!