Beyond Compare and WinMerge are pretty similar in purpose, so they should work well for comparing 2 files and showing you the changes. I use WinMerge, but have used Beyond Compare before.
While the UI may be different, it really shouldn't be too difficult to pick 2 files(or directories) to run a compare against to see what's different.
If there's a specific file you're looking at the changes for as well, you can also go onto the github repo, navigate to the file in the web view, and then click the little 'history' button on the upper right. That'll show a list of commits to the repo that affected that file(or directory). So you can also use that to figure out what changes have happened to get files up to speed.