You don't even need photoshop in this case. All he's doing is editing the base .txt file that the log came in and using a third party program, in this case Log Viewer, to open up the .txt file. Then he took a screenshot of it.
Editing the log file itself is ridiculously easy since it's only in a base .txt file. All you have to do is change whatever you need to in notepad and save it. Then use the same third party program he used and voila, you have Warbuck's screenshot in a nutshell.