With modern screen resolutions and pixel art, you're going to need to do some sort of scaling to get the big pixels.
I haven't used Construct before, so I can't give specific advice about that, but in general I would rather scale the pixel art in-engine rather than resizing the actual resources. I would be surprised if Construct doesn't have some way to do this, so you may want to ask in their forums about how other developers go about making pixel art games in that engine.
It may be that they actually do scale the resources themselves, in which case you're right: just scale up the resources to the desired size in any image editor. Just make sure you scale in integers and without anti-aliasing so you don't get blurry or wonky pixels!