How do we submit engine changes via Github to Epic?

Alright, so I’ve downloaded the source code from Github. I was able to compile it without any issues. I made some small changes to the engine source code which I think would be valued by both Epic and the Unreal developer community. I tested it and it works great.
I created a commit in Github and tried to push it up to the repository. I added a nice description and was all ready to go, and I click on the “Sync” button to submit a request to merge my branch. However, I get the following error message:

“Sync failed: doesn’t seem to exist anymore. You may not have access, or it may have been deleted or renamed.”

So, the question: How do I submit my requested changes to Epic for inclusion in the next release of the UE4 engine? (4.7)