I came across this site unsplash and they post free high resolution pictures to use. I have a canon550D with the standard kit 18-55m and a 50mm lens. How are these high resolution pictures achieved? I use lightroom for some basic editing... any information or advice would be great.
some basic editing...
That's what makes the difference. They probably use not so basic editing like sharpening, local adjustments, etc and they probably also do not just apply some of it, but a lot.
To cut a long story short: These are not images that come straight out of the camera and your will not achieve such results with the camera and basic editing alone.